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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 
• How to write a good literature review 
• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

• Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 
• Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 
• Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 
• Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 
• Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 
• Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

How to write a good literature review

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. 

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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How To Structure Your Literature Review

3 options to help structure your chapter.

By: Amy Rommelspacher (PhD) | Reviewer: Dr Eunice Rautenbach | November 2020 (Updated May 2023)

Writing the literature review chapter can seem pretty daunting when you’re piecing together your dissertation or thesis. As  we’ve discussed before , a good literature review needs to achieve a few very important objectives – it should:

• Demonstrate your knowledge of the research topic
• Identify the gaps in the literature and show how your research links to these
• Provide the foundation for your conceptual framework (if you have one)
• Inform your own  methodology and research design

To achieve this, your literature review needs a well-thought-out structure . Get the structure of your literature review chapter wrong and you’ll struggle to achieve these objectives. Don’t worry though – in this post, we’ll look at how to structure your literature review for maximum impact (and marks!).

But wait – is this the right time?

Deciding on the structure of your literature review should come towards the end of the literature review process – after you have collected and digested the literature, but before you start writing the chapter. 

In other words, you need to first develop a rich understanding of the literature before you even attempt to map out a structure. There’s no use trying to develop a structure before you’ve fully wrapped your head around the existing research.

Equally importantly, you need to have a structure in place before you start writing , or your literature review will most likely end up a rambling, disjointed mess. 

Importantly, don’t feel that once you’ve defined a structure you can’t iterate on it. It’s perfectly natural to adjust as you engage in the writing process. As we’ve discussed before , writing is a way of developing your thinking, so it’s quite common for your thinking to change – and therefore, for your chapter structure to change – as you write. 

Need a helping hand?

Like any other chapter in your thesis or dissertation, your literature review needs to have a clear, logical structure. At a minimum, it should have three essential components – an  introduction , a  body   and a  conclusion . 

Let’s take a closer look at each of these.

1: The Introduction Section

Just like any good introduction, the introduction section of your literature review should introduce the purpose and layout (organisation) of the chapter. In other words, your introduction needs to give the reader a taste of what’s to come, and how you’re going to lay that out. Essentially, you should provide the reader with a high-level roadmap of your chapter to give them a taste of the journey that lies ahead.

Here’s an example of the layout visualised in a literature review introduction:

Your introduction should also outline your topic (including any tricky terminology or jargon) and provide an explanation of the scope of your literature review – in other words, what you  will   and  won’t   be covering (the delimitations ). This helps ringfence your review and achieve a clear focus . The clearer and narrower your focus, the deeper you can dive into the topic (which is typically where the magic lies). 

Depending on the nature of your project, you could also present your stance or point of view at this stage. In other words, after grappling with the literature you’ll have an opinion about what the trends and concerns are in the field as well as what’s lacking. The introduction section can then present these ideas so that it is clear to examiners that you’re aware of how your research connects with existing knowledge .

2: The Body Section

The body of your literature review is the centre of your work. This is where you’ll present, analyse, evaluate and synthesise the existing research. In other words, this is where you’re going to earn (or lose) the most marks. Therefore, it’s important to carefully think about how you will organise your discussion to present it in a clear way. 

The body of your literature review should do just as the description of this chapter suggests. It should “review” the literature – in other words, identify, analyse, and synthesise it. So, when thinking about structuring your literature review, you need to think about which structural approach will provide the best “review” for your specific type of research and objectives (we’ll get to this shortly).

There are (broadly speaking)  three options  for organising your literature review.

Option 1: Chronological (according to date)

Organising the literature chronologically is one of the simplest ways to structure your literature review. You start with what was published first and work your way through the literature until you reach the work published most recently. Pretty straightforward.

The benefit of this option is that it makes it easy to discuss the developments and debates in the field as they emerged over time. Organising your literature chronologically also allows you to highlight how specific articles or pieces of work might have changed the course of the field – in other words, which research has had the most impact . Therefore, this approach is very useful when your research is aimed at understanding how the topic has unfolded over time and is often used by scholars in the field of history. That said, this approach can be utilised by anyone that wants to explore change over time .

For example , if a student of politics is investigating how the understanding of democracy has evolved over time, they could use the chronological approach to provide a narrative that demonstrates how this understanding has changed through the ages.

Here are some questions you can ask yourself to help you structure your literature review chronologically.

• What is the earliest literature published relating to this topic?
• How has the field changed over time? Why?
• What are the most recent discoveries/theories?

In some ways, chronology plays a part whichever way you decide to structure your literature review, because you will always, to a certain extent, be analysing how the literature has developed. However, with the chronological approach, the emphasis is very firmly on how the discussion has evolved over time , as opposed to how all the literature links together (which we’ll discuss next ).

Option 2: Thematic (grouped by theme)

The thematic approach to structuring a literature review means organising your literature by theme or category – for example, by independent variables (i.e. factors that have an impact on a specific outcome).

As you’ve been collecting and synthesising literature , you’ll likely have started seeing some themes or patterns emerging. You can then use these themes or patterns as a structure for your body discussion. The thematic approach is the most common approach and is useful for structuring literature reviews in most fields.

For example, if you were researching which factors contributed towards people trusting an organisation, you might find themes such as consumers’ perceptions of an organisation’s competence, benevolence and integrity. Structuring your literature review thematically would mean structuring your literature review’s body section to discuss each of these themes, one section at a time.

Here are some questions to ask yourself when structuring your literature review by themes:

• Are there any patterns that have come to light in the literature?
• What are the central themes and categories used by the researchers?
• Do I have enough evidence of these themes?

PS – you can see an example of a thematically structured literature review in our literature review sample walkthrough video here.

Option 3: Methodological

The methodological option is a way of structuring your literature review by the research methodologies used . In other words, organising your discussion based on the angle from which each piece of research was approached – for example, qualitative , quantitative or mixed  methodologies.

Structuring your literature review by methodology can be useful if you are drawing research from a variety of disciplines and are critiquing different methodologies. The point of this approach is to question  how  existing research has been conducted, as opposed to  what  the conclusions and/or findings the research were.

For example, a sociologist might centre their research around critiquing specific fieldwork practices. Their literature review will then be a summary of the fieldwork methodologies used by different studies.

Here are some questions you can ask yourself when structuring your literature review according to methodology:

• Which methodologies have been utilised in this field?
• Which methodology is the most popular (and why)?
• What are the strengths and weaknesses of the various methodologies?
• How can the existing methodologies inform my own methodology?

3: The Conclusion Section

Once you’ve completed the body section of your literature review using one of the structural approaches we discussed above, you’ll need to “wrap up” your literature review and pull all the pieces together to set the direction for the rest of your dissertation or thesis.

The conclusion is where you’ll present the key findings of your literature review. In this section, you should emphasise the research that is especially important to your research questions and highlight the gaps that exist in the literature. Based on this, you need to make it clear what you will add to the literature – in other words, justify your own research by showing how it will help fill one or more of the gaps you just identified.

Last but not least, if it’s your intention to develop a conceptual framework for your dissertation or thesis, the conclusion section is a good place to present this.

Example: Thematically Structured Review

In the video below, we unpack a literature review chapter so that you can see an example of a thematically structure review in practice.

Let’s Recap

In this article, we’ve  discussed how to structure your literature review for maximum impact. Here’s a quick recap of what  you need to keep in mind when deciding on your literature review structure:

• Just like other chapters, your literature review needs a clear introduction , body and conclusion .
• The introduction section should provide an overview of what you will discuss in your literature review.
• The body section of your literature review can be organised by chronology , theme or methodology . The right structural approach depends on what you’re trying to achieve with your research.
• The conclusion section should draw together the key findings of your literature review and link them to your research questions.

If you’re ready to get started, be sure to download our free literature review template to fast-track your chapter outline.

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

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27 Comments

Great work. This is exactly what I was looking for and helps a lot together with your previous post on literature review. One last thing is missing: a link to a great literature chapter of an journal article (maybe with comments of the different sections in this review chapter). Do you know any great literature review chapters?

I agree with you Marin… A great piece

I agree with Marin. This would be quite helpful if you annotate a nicely structured literature from previously published research articles.

Awesome article for my research.

I thank you immensely for this wonderful guide

It is indeed thought and supportive work for the futurist researcher and students

Very educative and good time to get guide. Thank you

Great work, very insightful. Thank you.

Thanks for this wonderful presentation. My question is that do I put all the variables into a single conceptual framework or each hypothesis will have it own conceptual framework?

Thank you very much, very helpful

This is very educative and precise . Thank you very much for dropping this kind of write up .

Pheeww, so damn helpful, thank you for this informative piece.

I’m doing a research project topic ; stool analysis for parasitic worm (enteric) worm, how do I structure it, thanks.

comprehensive explanation. Help us by pasting the URL of some good “literature review” for better understanding.

great piece. thanks for the awesome explanation. it is really worth sharing. I have a little question, if anyone can help me out, which of the options in the body of literature can be best fit if you are writing an architectural thesis that deals with design?

I am doing a research on nanofluids how can l structure it?

Beautifully clear.nThank you!

Lucid! Thankyou!

Brilliant work, well understood, many thanks

I like how this was so clear with simple language 😊😊 thank you so much 😊 for these information 😊

Insightful. I was struggling to come up with a sensible literature review but this has been really helpful. Thank you!

You have given thought-provoking information about the review of the literature.

Thank you. It has made my own research better and to impart your work to students I teach

I learnt a lot from this teaching. It’s a great piece.

I am doing research on EFL teacher motivation for his/her job. How Can I structure it? Is there any detailed template, additional to this?

You are so cool! I do not think I’ve read through something like this before. So nice to find somebody with some genuine thoughts on this issue. Seriously.. thank you for starting this up. This site is one thing that is required on the internet, someone with a little originality!

I’m asked to do conceptual, theoretical and empirical literature, and i just don’t know how to structure it

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

Literature Reviews

What this handout is about.

This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Introduction

OK. You’ve got to write a literature review. You dust off a novel and a book of poetry, settle down in your chair, and get ready to issue a “thumbs up” or “thumbs down” as you leaf through the pages. “Literature review” done. Right?

Wrong! The “literature” of a literature review refers to any collection of materials on a topic, not necessarily the great literary texts of the world. “Literature” could be anything from a set of government pamphlets on British colonial methods in Africa to scholarly articles on the treatment of a torn ACL. And a review does not necessarily mean that your reader wants you to give your personal opinion on whether or not you liked these sources.

What is a literature review, then?

A literature review discusses published information in a particular subject area, and sometimes information in a particular subject area within a certain time period.

A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts. In a research paper, you use the literature as a foundation and as support for a new insight that you contribute. The focus of a literature review, however, is to summarize and synthesize the arguments and ideas of others without adding new contributions.

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone. For professionals, they are useful reports that keep them up to date with what is current in the field. For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper’s investigation. Comprehensive knowledge of the literature of the field is essential to most research papers.

Who writes these things, anyway?

Literature reviews are written occasionally in the humanities, but mostly in the sciences and social sciences; in experiment and lab reports, they constitute a section of the paper. Sometimes a literature review is written as a paper in itself.

Let’s get to it! What should I do before writing the literature review?

If your assignment is not very specific, seek clarification from your instructor:

• Roughly how many sources should you include?
• What types of sources (books, journal articles, websites)?
• Should you summarize, synthesize, or critique your sources by discussing a common theme or issue?
• Should you evaluate your sources?
• Should you provide subheadings and other background information, such as definitions and/or a history?

Find models

Look for other literature reviews in your area of interest or in the discipline and read them to get a sense of the types of themes you might want to look for in your own research or ways to organize your final review. You can simply put the word “review” in your search engine along with your other topic terms to find articles of this type on the Internet or in an electronic database. The bibliography or reference section of sources you’ve already read are also excellent entry points into your own research.

Narrow your topic

There are hundreds or even thousands of articles and books on most areas of study. The narrower your topic, the easier it will be to limit the number of sources you need to read in order to get a good survey of the material. Your instructor will probably not expect you to read everything that’s out there on the topic, but you’ll make your job easier if you first limit your scope.

Keep in mind that UNC Libraries have research guides and to databases relevant to many fields of study. You can reach out to the subject librarian for a consultation: https://library.unc.edu/support/consultations/ .

And don’t forget to tap into your professor’s (or other professors’) knowledge in the field. Ask your professor questions such as: “If you had to read only one book from the 90’s on topic X, what would it be?” Questions such as this help you to find and determine quickly the most seminal pieces in the field.

Consider whether your sources are current

Some disciplines require that you use information that is as current as possible. In the sciences, for instance, treatments for medical problems are constantly changing according to the latest studies. Information even two years old could be obsolete. However, if you are writing a review in the humanities, history, or social sciences, a survey of the history of the literature may be what is needed, because what is important is how perspectives have changed through the years or within a certain time period. Try sorting through some other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to consider what is currently of interest to scholars in this field and what is not.

Strategies for writing the literature review

Find a focus.

A literature review, like a term paper, is usually organized around ideas, not the sources themselves as an annotated bibliography would be organized. This means that you will not just simply list your sources and go into detail about each one of them, one at a time. No. As you read widely but selectively in your topic area, consider instead what themes or issues connect your sources together. Do they present one or different solutions? Is there an aspect of the field that is missing? How well do they present the material and do they portray it according to an appropriate theory? Do they reveal a trend in the field? A raging debate? Pick one of these themes to focus the organization of your review.

Convey it to your reader

A literature review may not have a traditional thesis statement (one that makes an argument), but you do need to tell readers what to expect. Try writing a simple statement that lets the reader know what is your main organizing principle. Here are a couple of examples:

The current trend in treatment for congestive heart failure combines surgery and medicine. More and more cultural studies scholars are accepting popular media as a subject worthy of academic consideration.

Consider organization

You’ve got a focus, and you’ve stated it clearly and directly. Now what is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? And in what order should you present them? Develop an organization for your review at both a global and local level:

First, cover the basic categories

Just like most academic papers, literature reviews also must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper. The following provides a brief description of the content of each:

• Introduction: Gives a quick idea of the topic of the literature review, such as the central theme or organizational pattern.
• Body: Contains your discussion of sources and is organized either chronologically, thematically, or methodologically (see below for more information on each).
• Conclusions/Recommendations: Discuss what you have drawn from reviewing literature so far. Where might the discussion proceed?

Organizing the body

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario:

You’ve decided to focus your literature review on materials dealing with sperm whales. This is because you’ve just finished reading Moby Dick, and you wonder if that whale’s portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980’s. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Now consider some typical ways of organizing the sources into a review:

• Chronological: If your review follows the chronological method, you could write about the materials above according to when they were published. For instance, first you would talk about the British biological studies of the 18th century, then about Moby Dick, published in 1851, then the book on sperm whales in other art (1968), and finally the biology articles (1980s) and the recent articles on American whaling of the 19th century. But there is relatively no continuity among subjects here. And notice that even though the sources on sperm whales in other art and on American whaling are written recently, they are about other subjects/objects that were created much earlier. Thus, the review loses its chronological focus.
• By publication: Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on biological studies of sperm whales if the progression revealed a change in dissection practices of the researchers who wrote and/or conducted the studies.
• By trend: A better way to organize the above sources chronologically is to examine the sources under another trend, such as the history of whaling. Then your review would have subsections according to eras within this period. For instance, the review might examine whaling from pre-1600-1699, 1700-1799, and 1800-1899. Under this method, you would combine the recent studies on American whaling in the 19th century with Moby Dick itself in the 1800-1899 category, even though the authors wrote a century apart.
• Thematic: Thematic reviews of literature are organized around a topic or issue, rather than the progression of time. However, progression of time may still be an important factor in a thematic review. For instance, the sperm whale review could focus on the development of the harpoon for whale hunting. While the study focuses on one topic, harpoon technology, it will still be organized chronologically. The only difference here between a “chronological” and a “thematic” approach is what is emphasized the most: the development of the harpoon or the harpoon technology.But more authentic thematic reviews tend to break away from chronological order. For instance, a thematic review of material on sperm whales might examine how they are portrayed as “evil” in cultural documents. The subsections might include how they are personified, how their proportions are exaggerated, and their behaviors misunderstood. A review organized in this manner would shift between time periods within each section according to the point made.
• Methodological: A methodological approach differs from the two above in that the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the “methods” of the researcher or writer. For the sperm whale project, one methodological approach would be to look at cultural differences between the portrayal of whales in American, British, and French art work. Or the review might focus on the economic impact of whaling on a community. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed. Once you’ve decided on the organizational method for the body of the review, the sections you need to include in the paper should be easy to figure out. They should arise out of your organizational strategy. In other words, a chronological review would have subsections for each vital time period. A thematic review would have subtopics based upon factors that relate to the theme or issue.

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

• Current Situation: Information necessary to understand the topic or focus of the literature review.
• History: The chronological progression of the field, the literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Methods and/or Standards: The criteria you used to select the sources in your literature review or the way in which you present your information. For instance, you might explain that your review includes only peer-reviewed articles and journals.

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

Begin composing

Once you’ve settled on a general pattern of organization, you’re ready to write each section. There are a few guidelines you should follow during the writing stage as well. Here is a sample paragraph from a literature review about sexism and language to illuminate the following discussion:

However, other studies have shown that even gender-neutral antecedents are more likely to produce masculine images than feminine ones (Gastil, 1990). Hamilton (1988) asked students to complete sentences that required them to fill in pronouns that agreed with gender-neutral antecedents such as “writer,” “pedestrian,” and “persons.” The students were asked to describe any image they had when writing the sentence. Hamilton found that people imagined 3.3 men to each woman in the masculine “generic” condition and 1.5 men per woman in the unbiased condition. Thus, while ambient sexism accounted for some of the masculine bias, sexist language amplified the effect. (Source: Erika Falk and Jordan Mills, “Why Sexist Language Affects Persuasion: The Role of Homophily, Intended Audience, and Offense,” Women and Language19:2).

Use evidence

In the example above, the writers refer to several other sources when making their point. A literature review in this sense is just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence to show that what you are saying is valid.

Be selective

Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the review’s focus, whether it is thematic, methodological, or chronological.

Use quotes sparingly

Falk and Mills do not use any direct quotes. That is because the survey nature of the literature review does not allow for in-depth discussion or detailed quotes from the text. Some short quotes here and there are okay, though, if you want to emphasize a point, or if what the author said just cannot be rewritten in your own words. Notice that Falk and Mills do quote certain terms that were coined by the author, not common knowledge, or taken directly from the study. But if you find yourself wanting to put in more quotes, check with your instructor.

Summarize and synthesize

Remember to summarize and synthesize your sources within each paragraph as well as throughout the review. The authors here recapitulate important features of Hamilton’s study, but then synthesize it by rephrasing the study’s significance and relating it to their own work.

Keep your own voice

While the literature review presents others’ ideas, your voice (the writer’s) should remain front and center. Notice that Falk and Mills weave references to other sources into their own text, but they still maintain their own voice by starting and ending the paragraph with their own ideas and their own words. The sources support what Falk and Mills are saying.

Use caution when paraphrasing

When paraphrasing a source that is not your own, be sure to represent the author’s information or opinions accurately and in your own words. In the preceding example, Falk and Mills either directly refer in the text to the author of their source, such as Hamilton, or they provide ample notation in the text when the ideas they are mentioning are not their own, for example, Gastil’s. For more information, please see our handout on plagiarism .

Revise, revise, revise

Draft in hand? Now you’re ready to revise. Spending a lot of time revising is a wise idea, because your main objective is to present the material, not the argument. So check over your review again to make sure it follows the assignment and/or your outline. Then, just as you would for most other academic forms of writing, rewrite or rework the language of your review so that you’ve presented your information in the most concise manner possible. Be sure to use terminology familiar to your audience; get rid of unnecessary jargon or slang. Finally, double check that you’ve documented your sources and formatted the review appropriately for your discipline. For tips on the revising and editing process, see our handout on revising drafts .

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Anson, Chris M., and Robert A. Schwegler. 2010. The Longman Handbook for Writers and Readers , 6th ed. New York: Longman.

Jones, Robert, Patrick Bizzaro, and Cynthia Selfe. 1997. The Harcourt Brace Guide to Writing in the Disciplines . New York: Harcourt Brace.

Lamb, Sandra E. 1998. How to Write It: A Complete Guide to Everything You’ll Ever Write . Berkeley: Ten Speed Press.

Rosen, Leonard J., and Laurence Behrens. 2003. The Allyn & Bacon Handbook , 5th ed. New York: Longman.

Troyka, Lynn Quittman, and Doug Hesse. 2016. Simon and Schuster Handbook for Writers , 11th ed. London: Pearson.

You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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Writing Literature Reviews: 4. Structure Your Lit Review

• What is a "Literature Review"?
• 1. Brainstorm
• 3. Refine Search and Topic
• 4. Structure Your Lit Review
• Helpful Sites

How to Structure Your Lit Review

A literature review, even when it is within a larger paper, should include an introduction, a main body section, and a conclusion.

In the Introduction Section :

• define your topic and scope
• explain the organization of your lit review

In the Main Section :

• Present the literature you found related to your topic in a clear, organized way
• Compare and contrast the literature
• Identify problems, issues, and debates among scholars on the topic

There are many ways to organize the main section of a literature review. Here are a few ways you could organize this section:

• Chronological - Present a condensed history of the major ideas and developments of a topic over time.
• Thematic - Present the major theories relevant to your topic and how they agree or contrast.
• Methodological - If there are different methods of research on your topic, you can organize your review by grouping the findings of different methodologies. Be sure to compare and contrast these methods (you are setting up an argument for your own methods.)
• Theoretical - Organize your review by the various theories others have developed relevant to the topic, comparing and contrasting the strengths and weaknesses of each.

In the Conclusion Section :

• Summarize your findings in the scholarly literature
• Identify any gaps and explain briefly how you are filling that gap with your own research (if appropriate)
• Explain how your paper/ideas/research relates to the greater scholarly literature and create a transition to the rest of your paper

Helpful Sites on Literature Reviews

Much of the information in this guide and more information can be found on the websites listed on the  Helpful Sites tab .

Ask A Librarian

Make an appointment

Chat with a Librarian

Email [email protected]

• << Previous: 3. Refine Search and Topic
• Next: Tools >>
• University of Colorado Boulder Libraries
• Research Guides
• Writing Literature Reviews
• Last Updated: Feb 29, 2024 3:43 PM
• URL: https://libguides.colorado.edu/litreview

Analysis and Synthesis

Body paragraphs: introduce, cite, explain.

In the Literature Review, each body paragraph should cover a single trend or gap in the research, using two or more sources to show the reader how that trend or gap emerges. Here, we will review a specific way of composing a paragraph that is often found in academic writing. This is not the only model you can use in writing, but it is a good starting point to help you develop your discussion of trends and gaps for the Literature Review.

In general, body paragraphs should have one specific point. Do not group several trends or gaps in the research in a single paragraph. For example, you would not want to divide your essay into a trends paragraph and a gaps paragraph. This idea may appear to be a paradox, but the narrower your paragraph’s point, the easier it is to write more. Aim for about half a page per paragraph. This makes it easier for your reader to follow your reasoning. There are three main components to a body paragraph: you’ll introduce the main idea (trend or gap), cite evidence from the sources to support it, and explain how the evidence you’ve presented fits together.

Your claim about the trend or gap in the research should be the focus of your topic sentence for your paragraph. You do not want to start with evidence, which means that you should never begin a paragraph with a quotation from a source. Instead, your first sentence should clearly identify the single trend or gap in the research that you want to discuss in that paragraph. Your reader will look at this claim in the first sentence and say, “Okay, now show me the evidence. Convince me.”

To support your claim, you need to cite specific evidence from two or more sources to demonstrate the trend and/or gap’s existence. You will want to vary the ways in which you incorporate that evidence, using a good mix of summary, paraphrase, and brief quotation.  Avoid long quotations from your sources in the Literature Review. This is a relatively short essay, and the vast majority of the words in it should be your own. The goal of this part of the paragraph is to show the reader how these sources converge to create or reveal this trend or gap.

In academic writing, we never allow evidence to speak for itself; we always explain its purpose. This is the explanation of your evidence. In practical terms, this means that you should never end a paragraph with a quotation. Instead, the last sentence of your paragraph should explain the evidence you have presented to the reader. This explanation should echo the claim made in the beginning of the paragraph. It will take practice to write a good explanation because you have to convince the reader that the evidence you’ve cited supports your claim. It is more than just restating the claim. You have to make the connections for us, like retracing your steps. How did that evidence lead you to identify that trend or gap?

applying research skills

A good metaphor to help you better understand the introduce, cite, explain (ICE) paragraph model is to think about a sport where a swing is used. For example, golf would be a great sport to use for this metaphor.

In golf, players must align themselves to the ball and get ready to strike it. In other words, they must prepare themselves to swing. This can be compared to the topic sentence because it is the set up for your body paragraph; it organizes what is to follow. In the same way, golfers must set themselves up to move the ball to the green.

Next, a golfer will need to actually swing the club, reaching back to gain momentum and speed before striking the ball. This would represent the evidence cited within the body paragraph to demonstrate that the trend and/or gap exists. Without striking the ball, a golfer is stuck.  A bad strike can also send the ball careening off-course, directly into a sand trap or water hazard.  In much the same way, citing inappropriate or insufficient evidence can derail your paragraph.

Finally, after striking the ball, it is imperative that golfers follow through to enable the ball to speed to the spot where they have directed it. This represents the explanation. Without an explanation, your claim and evidence will not go where you directed them; they will not make sense to the audience. For this reason, it is imperative that you provide your audience a good follow through by explaining how the evidence supports the claim.

research toolbox

In this research toolbox, please identify where the author introduces , cites , and explains in this sample paragraph from a literature review:

Current studies by Smith (2016), Cassidy and Doyle (2015), and Rogers, Mack, and Johnson (2017) indicate that consumers do not properly use nutrition labels because they do not understand them. Smith (2016) conducted a survey with 220 participants and found that 65% of those involved did not understand the layout and information included on nutrition labels. Cassidy and Doyle (2015) added to this conversation by stating that 54% of the 80 participants in their observation did not properly consult and understand the labels based on purchases and follow up interviews. Lastly, Rogers et al. (2017) found that 62% of the 140 participants in their survey selected incorrect answers to questions regarding nutrition labels and their information. All of these sources indicate the majority of consumers do not understand how to read and interpret nutrition labels properly; therefore, consumers are not using these labels as intended. This misuse demonstrates the need for either increased education on the layout and information presented on food labels or a redesign of food labels to make them more accessible to the average consumer.

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The Literature Review: 5. Organizing the Literature Review

• 1. Introduction
• 2. Why Do a Literature Review?
• 3. Methods for Searching the Literature
• 4. Analysing the Literature
• 5. Organizing the Literature Review
• 6. Writing the Review

1. Organizing Principles

A literature review is a piece of discursive prose, not a list describing or summarizing one piece of literature after another. It should have a single organizing principle:

• Thematic - organize around a topic or issue
• Chronological - sections for each vital time period
• Methodological - focus on the methods used by the researchers/writers

4. Selected Online Resources

• Literature Review in Education & Behavioral Sciences This is an interactive tutorial from Adelphi University Libraries on how to conduct a literature review in education and the behavioural sciences using library databases
• Writing Literature Reviews This tutorial is from the Writing section of Monash University's Language and Learning Online site
• The Literature Review: A Few Tips on Conducting It This guide is from the Health Services Writing Centre at the University of Toronto
• Learn How to Write a Review of the Literature This guide is part of the Writer's Handbook provided by the Writing Center at the University of Wisconsin-Madison

2. Structure of the Literature Review

Although your literature review will rely heavily on the sources you read for its information, you should dictate the structure of the review. It is important that the concepts are presented in an order that makes sense of the context of your research project.

There may be clear divisions on the sets of ideas you want to discuss, in which case your structure may be fairly clear. This is an ideal situation. In most cases, there will be several different possible structures for your review.

Similarly to the structure of the research report itself, the literature review consists of:

• Introduction

Introduction - profile of the study

• Define or identify the general topic to provide the context for reviewing the literature
• Outline why the topic is important
• Identify overall trends in what has been published about the topic
• Identify conflicts in theory, methodology, evidence, and conclusions
• Identify gaps in research and scholarlship
• Explain the criteria to be used in analysing and comparing the literature
• Describe the organization of the review (the sequence)
• If necessary, state why certain literature is or is not included (scope)

Body - summative, comparative, and evaluative discussion of literature reviewed

For a thematic review:

• organize the review into paragraphs that present themes and identify trends relevant to your topic
• each paragraph should deal with a different theme - you need to synthesize several of your readings into each paragraph in such a way that there is a clear connection between the sources
• don't try to list all the materials you have identified in your literature search

From each of the section summaries:

• summarize the main agreements and disagreements in the literature
• summarize the general conclusions that have been drawn
• establish where your own research fits in the context of the existing literature

5. A Final Checklist

• Have you indicated the purpose of the review?
• Have you emphasized recent developments?
• Is there a logic to the way you organized the material?
• Does the amount of detail included on an issue relate to its importance?
• Have you been sufficiently critical of design and methodological issues?
• Have you indicated when results were conflicting or inconclusive and discussed possible reasons?
• Has your summary of the current literature contributed to the reader's understanding of the problems?

3. Tips on Structure

A common error in literature reviews is for writers to present material from one author, followed by information from another, then another.... The way in which you group authors and link ideas will help avoid this problem. To group authors who draw similar conclusions, you can use linking words such as:

• additionally

When authors disagree, linking words that indicate contrast will show how you have analysed their work. Words such as:

• on the other hand
• nonetheless

will indicate to your reader how you have analysed the material. At other times, you may want to qualify an author's work (using such words as specifically, usually, or generally ) or use an example ( thus, namely, to illustrate ). In this way you ensure that you are synthesizing the material, not just describing the work already carried out in your field.

Another major problem is that literature reviews are often written as if they stand alone, without links to the rest of the paper. There needs to be a clear relationship between the literature review and the methodology to follow.

• << Previous: 4. Analysing the Literature
• Next: 6. Writing the Review >>
• Last Updated: Feb 8, 2022 5:25 PM
• URL: https://libguides.uwi.edu/litreviewsoe

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• Dissertation
• What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

Prevent plagiarism, run a free check.

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

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3 Literature Review

Charitianne Williams

By the end of this chapter, you will be able to do the following:

• Understand the purpose and function of a literature review.
• Structure a literature review according to basic genre expectations.
• Synthesize ideas from multiple sources using a synthesis matrix.
• Choose between narrative or parenthetical citation and direct quoting, or paraphrase with intent and purpose.

I. Introduction

The purpose of a literature review is just that—it reviews. This means that literature reviews examine a text after it was produced, with all the benefits that hindsight allows a reader. In popular culture, we commonly review movies, restaurants, vacation spots, products, etc. In those reviews, you look back at the single thing you are reviewing and your experience with it. You focus on the strengths and weaknesses of your experience and judge the experience as positive or negative while recommending or not recommending the place or product and explaining why.

An academic literature review does something different, although some of the skills and strategies you use remain the same. The job of a literature review is to examine a collection of research or scholarship (not a single thing or text) on a given topic and show how that scholarship fits together. Literature reviews summarize, describe, evaluate, and synthesize the work of other authors and researchers while looking for common trends/patterns, themes, inconsistencies, and gaps in this previous research. The main strategy writers of a literature review use is synthesis.

SYNTHESIS: the combination of ideas and elements to form a complete system or theory.

A good metaphor for synthesis is cooking! Imagine the ingredients for a loaf of bread laid out on a kitchen cabinet. Each ingredient—eggs, milk, flour, sugar, salt, yeast—have their own purpose and can be combined in different ways to form food other than bread. Knowing all of those individual attributes that make an egg an egg, or the difference between yeast and flour, is what makes you a chef. When you combine all these ingredients according to the recipe, you get something different than all the ingredients on their own: and most of us would rather eat a slice of bread than a spoonful of flour. The product of synthesis is like bread. Synthesis takes a list of ingredients and makes them into something more than the ingredients alone.

Usually, the writers of a literature review will start with a question that they want to answer through informed and research-based evidence gathered while reading others’ work on related topics. The “thesis” or controlling idea of a literature review may be that same question ( “This review seeks to answer…” ) or it may be a statement describing the reviewed research. The thesis reflects the purpose of the literature review as a genre and is different from the thesis you will write for the research paper that argues a claim or asserts a new idea.

Example 3.1: Look at this thesis statement taken from the introduction of a literature review in environmental psychology on the relationship between “nature sounds” and restorative environments:

From this example, we can learn many things about literature reviews:

• They are explicit and focused on their topic. The opening states an observable truth about the current research ( emphasizes nature ), is followed by a general condition ( positive psychological experiences) within that research, and then finally focuses on describing how a particular outcome is achieved (listening to nature sounds is restorative).
• They seek to pre vent or eliminate misunderstanding. Note the use of specialized key terms, exacting transitional phrases, and meaningful verbs in the thesis such as “ restorative environments,” “in particular,” and “ generate .”
• They seek to forward understanding. In other words, literature reviews examine and link together evidence described and validated in the research of others so a reader can learn how a field is developing. ( Research seems to agree that nature sounds can relieve stress and fatigue–this review will examine that conclusion so readers can understand/ build on how and why.)

Moving from the beginning to the very end of the literature review, we can also learn many things about literature reviews from the sources used. Think of each text listed in the References section of a literature review as contributing pieces to a gigantic puzzle.

Example 3.2: Look at the first three articles listed in the References for the article excerpted above:

Abbott, L. C., Taff, D., Newman, P., Benfield, J. A., and Mowen, A. J. (2016). The influence of natural sounds on attention restoration. J. Park Recreation Adm. 34, 5–15. doi: 10.18666/JPRA-2016-V34-I3-6893

Aletta, F., and Kang, J. (2019). Promoting healthy and supportive acoustic environments: going beyond the quietness. Int. J. Environ. Res. Public Health 16:4988. doi: 10.3390/ijerph16244988

Aletta, F., Oberman, T., and Kang, J. (2018). Associations between positive health-related effects and soundscapes perceptual constructs: a systematic review. Int. J. Environ. Res. Public Health 15:2392. doi: 10.3390/ijerph15112392

None of these sources are exactly the same. One focuses on sound and attention, the next two on sound and health, and none of them are quite the same as sound and restoration —but they are all pieces of the puzzle that give a full understanding of how sound and restorative environments relate.

As the author of the literature review, it is your job to join the pieces together, giving your reader a complete picture of what researchers know about your topic.

Literature reviews are an indispensable tool for researchers. Instead of having to read dozens of articles on a topic, a researcher could instead read a literature review that synthesizes what is known and puts each piece of scholarship into conversation with the others. This could be not only quicker, but also more valuable.

Have you heard the saying that the whole is more than the sum of its parts? The knowledge constructed by a well-written literature review often outweighs the knowledge constructed by simply reading each article in the References section on its own because the author of a literature review processes and analyzes the information for the reader.

Literature reviews occur in two general forms—as a background section in a scholarly work or as a stand-alone genre in and of itself. In both situations, the basic purpose and structure of the literature review is similar: it is the length and the scope that varies. For example, consider the previous chapter, the Proposal. In most proposals, you will want to convince your audience that you are informed on the background of your topic—a literature review is how you would do that. Since a proposal is commonly a short text, you do not have the space to summarize every piece of research. You must select an important set and synthesize that information into a small section signaling your expertise.

On the other hand, consider a professional journal intended to keep its readers up to date on new technologies and findings in a specific field or career. New ideas and discoveries are emerging every day, and it can be difficult to stay on top of all of these new findings, understand how they fit together, and also keep track of your own career responsibilities! A magazine might hire an author to read all the new research on a specific topic and synthesize it into a single article, a state-of-the-art review, so that practitioners in a field can read a single 25-page article instead of 100 25-page articles.

More Resources 3.1: Literature Reviews

II. Rhetorical Considerations: Voice

Using the scholarship of other writers and researchers is one of the things that differentiates academic writing from other types of writing. Using others’ scholarship in a meaningful way that creates new knowledge without mischaracterizing the original findings takes effort, attention, and usually several rounds of revision and rewriting. One of the issues is voice , which refers to the attitude and tone of a text—think of it as what the text “sounds like” in your head as you read it. Voice is an important element of cohesion , or what some people think of as “flow.” Creating a consistent voice in the mind of your reader helps them fit all the information in a text together in the way the author intends. Check out this advice from APAstyle.org about academic style and voice.

Think back to your annotated bibliography and how you created your summaries. You probably used key terms from the original authors’ texts, but because you had to take whole articles and restate the meaning in a short paragraph, there wasn’t room to just repeat the words of the original author. So you had to write the summaries in your voice . If you used those key terms correctly and in ways similar to original authors, those key terms probably did not interfere with cohesiveness and voice. However, in the literature review, you have many more voices to synthesize than you did to summarize in the annotated bibliography. Maintaining a consistent and cohesive voice will be challenging. An important way to maintain voice is through paraphrasing, discussed later in this chapter.

More Resources 3.2: Transitions

Another important way to maintain cohesion is through the use of metadiscourse (see Chapter 2) and transitional phrases. See this link for the use and meaning of transitional phrases, sometimes called signposts .

III. The Literature Review Across the Disciplines

Example 3.3: Academic and Professional Examples

Structure of Literature Reviews

While the details vary across disciplines, all literature reviews tend to have similar basic structure. The introduction of a literature review informs the reader on the topic by defining key terms, citing key researchers or research periods in the field, and introducing the main focus of the review in a descriptive thesis statement. The introduction also explains the organization of the review. In a literature review, you organize your discussion of the research by topic or theme— not article or author. This is in direct contrast to the annotated bibliography, which is often the first step in the writing process for a literature review.

In the annotated bibliography, you organize your entries in alphabetical order by authors’ last names. Each annotation is directly connected to a single text. A literature review is connected to a collection of texts, and therefore must be organized in a way that reflects this.

Example 3.4: Let’s examine the full paragraph that the thesis statement we analyzed earlier came from:

A systematic review by Aletta et al. (2018) has identified links between positive urban soundscapes (which may also include nature sounds) and health and well-being, including stress recovery. Given the emphasis on nature w ithin restorative environments (see Hartig et al., 2014 ), the present narrative literature review focuses on evidence for positive psychological experiences of nature sounds and soundscapes specifically, and in particular how listening to these can generate perceptions and outcomes of restoration from stress and fatigue. This review has five key objectives, summarized in Figure 1 [in the article] . First, it explores literature regarding the impact of nature sounds on perceptions and experiences of wider natural environments. Second, it examines evidence regarding cognitive and affective appraisals of nature sounds and their contributions to overall perceptions of restorative environments. Third, literature regarding restorative outcomes in response to nature sounds is assessed. Fourth, the relevance of key restoration theories to this top ic is examined and areas where these theories are limited are identified. Fifth, a possible new theoretical area of interest—semantic associations with nature—is discussed and exemplified by recent acoustics research (Ratcliffe, 2021, emphasis added).

Notice how the thesis statement (in bold ) is followed by an explicit description of the five key objectives—which correspond to the titles (usually called headings ) of the five major sections of the body of the literature review. The introduction basically outlines the body of the literature review to make it easier for a researcher to find the specific information they are looking for. What follows each of these headings is an analysis and synthesis of the topic described in the heading—which is what we mean when we say a literature review is organized by topic.

Example 3.5: See how the body sections of a literature review synthesize research and evidence in relation to a focused topic. Read this example taken from a literature review in another discipline, nursing.

The introduction states that the review’s purpose is to understand the issues facing nurses in situations such as the COVID-19 pandemic. The researchers found several themes in the research that all contributed to nurses’ experiences. This paragraph describes one of those themes which the authors label “Professional collegiality”:

3.2.2. Professional collegiality

Professional camaraderie amongst nursing colleagues working during a pandemic was high (Ives et al., 2009, Kim, 2018, Liu a nd Liehr , 2009). Nurses acknowledged the importance of caring for their co-workers and in sharing the load. Some nurses associated the experience with working on a battlefield, whereby they worked together as a team protecting one another (Chung et al., 20 05, Kang et al., 2018, Liu and Liehr , 2009). Appreciation of their nursing colleagues was demonstrated through sharing their experiences, willingness to work together and encouraging a team spirit (Shih et al., 2007, Chung et al., 2005, Chiang et al., 2007 ). (Ratcliffe, 2021, p.4)

In this single paragraph, there are seven different research articles cited, and some of them are cited twice. There is no way to write a coherent paragraph summarizing seven different research articles at once—instead, the authors of this paragraph reviewed what the researchers said about collegiality, found where their findings pointed in the same direction, and put those connections into their own words. This is the importance of the review’s body section: it is here where you really dig into the content, meaning, and implications of the scholarship you are discussing.

The end of a literature review looks different from the one- or two-paragraph conclusion we are used to in other texts. The end is often made up of multiple sections, each with a slightly different purpose, although all are probably recognizable to you. A “Discussion” section is almost always present, where the author summarizes the most important findings of each section. In most cases, the “Discussion” section does not contain new information, but ties the different body sections together in ways that provide a deeper analysis.

The end of a literature review may also contain an “Implications for Future Research” or “Resolution” after the Discussion—sometimes this final section is even called “Conclusion.” What this last section looks like is often dependent upon the type of review you are writing, and whether the review is standing alone as a complete text or part of a larger project.

In any situation, across all disciplines, it is important to understand how your literature review is meant to inform the reader and what kind of review is appropriate for the context, in order to decide how you should structure the beginning and end of your review.

Types of Literature Reviews

There are different types of literature reviews, although in undergraduate study the Traditional or Narrative Review is most common. Narrative reviews are somewhat exploratory in their content—in a narrative review you are synthesizing the results of specific texts selected for their connection to your topic. Narrative reviews almost always end with a section describing areas for future research if they are a stand-alone text, or a section describing why the author’s research is so needed if part of a larger research article. The chart below outlines the key differences between three major literature review types. Notice that each type has a slightly different purpose. You might think about which type best fits your project as you read.

Table 3.1: Types of Literature Reviews

More Resources 3.3: Literature Review Structures

IV. Research Strategies: Developing a Methodology

Systematic and scoping reviews should always contain a Research Methodology that explains to your reader exactly how you found the research you are reviewing. Often Narrative Reviews will also contain a research methodology, although it will be slightly different since they are not comprehensive reviews, meaning, they do not attempt to find all the research on a topic—by design, they cover only a specific portion. Even if you are not required to write up your methodology, you need clear research strategies to find the appropriate scholarship for your literature review.

Example 3.6: Check out this excerpt from the methods sections from a psychology literature review. Note how the authors clearly describe what types of sources they’ll be using as well as their steps throughout the research process.

Drawing on individual case studies, archival reports, correlational studies, and laboratory and field experiments, this monograph scrutinizes a sequence of events during which confessions may be obtained from criminal suspects and used as evidence. First, we examine the pre-interrogation interview, a process by which police …( Kassin and Gudjonsson , 2004, p.33)

Example 3.7: Here is another example from the field of education. In it the authors describe two separate searches they performed to gather the literature—the first search used key terms they decided upon before reading any scholarship, and the second search used the terms that they found were common to that first set of texts (see more about key terms here and in the Annotated Bibliography chapter).

We conducted two rounds of literature searches, utilizing the following databases: World CAT (general search), EB SCO Academic Search Complete, EBSCO Education Source, and Linguistics and Language Behavior Abstracts (ProQuest). In the first round, we searched using every possible combination of the following terms: ‘race,’ ‘language teaching,’ ‘ethnicity,’ ‘language p edagogy,’ ‘Whiteness,’ ‘racialized,’ ‘antiracism,’ and ‘ nativeness .’ For the second round of our literature search, we searched using terms that we saw emerging from the literature such as ‘racial identities of language learners,’ ‘racial identities of lan guage teachers,’ ‘language varieties and language teaching,’ ‘race and language teacher education,’ ‘race and educational policy,’ ‘race and language programs,’ and ‘race and language curriculum’ and also repeated our earlier searches in order to keep the literature updated. (Von Esch et al., 2020, p. 392)

No matter the type of research (see a description of qualitative vs. quantitative research ), the specific genres (see descriptions of academic research genres ), or the time frame (see a discussion on the importance of publication date ) you use for your review, it is important to think through the options, make a decision, and incorporate all your research knowledge—use of key terms, use of subject filters, use of specialized databases, etc.—into a coherent and meaningful process that results in the best scholarship for your inquiry and review.

Here’s a video to help you get started on using databases for research:

Library Referral: Connecting the Conversation with Scholarly Sources and Beyond​

(by Annie R. Armstrong)

Research involves drawing from numerous voices from a range of source types. The sources you choose to include in your conversation are context-specific and might vary depending on your topic or the parameters of your assignment. Review your assignment description and talk to your instructor about guidelines. While most research papers emphasize scholarly sources, expertise isn’t always equated with scholarliness and you might want to branch out. For example, a research paper focusing on exploitation of Native American land and communities by the mining industry should make some attempt to include sources generated by the communities under discussion, especially if their point of view is not represented in the peer-reviewed, scholarly sources you’ve found. Think about who the stakeholders are as related to various aspects of your topic and how you can tap into their voices through available resources. You may want to consult a librarian about this.

The chart below summarizes the breadth of source types available through library websites versus the open web:

Table 3.2: Scholarly Sources and Beyond

V. Reading Strategies: Intertextuality and Graphic Organizers

Typically we think of reading as something we do to learn the content of a text—and this is absolutely true! But true understanding means knowing the relationships between and impact of separate but related topics, which might mean understanding how different texts—generally focused on one topic—overlap or differ.

Intertextuality refers to the connections that exist between texts. Intertextuality as a reading strategy means looking for the connections between the text you are reading and others you have already read; anticipating connections with other texts that you have not yet read, but plan to; as well as connections to whole disciplines, fields, and social phenomena. Reading for intertextuality means looking for opportunities to connect texts with each other, and keeping track of those connections in a productive way.

This means note-taking is essential to intertextual reading. Once you have thought carefully about why you are reading a text, what types of information to look for, and what you will do with that information, you can better decide how to keep track of that information. In regards to literature reviews, one type of graphic organizer dominates: the Synthesis Matrix.

The synthesis matrix is a way to keep track of the themes, concepts, and patterns that are emerging from your reading—NOT all the individual content of each article. This is important, yes, and you will need the citations, but literature reviews move one step further into the topic than simply identifying the pieces. You will need to synthesize.

If you have an annotated bibliography of sources already, it is the perfect way to start your synthesis matrix. An annotated bibliography is often the first step in preparing for a literature review, and is quite similar to an ingredient list, if we are using the metaphor from the introduction. (For a detailed description of how to write an annotated bibliography, see Chapter 1 ).

In your annotations, you will have selected the most important information that text supplies in relation to your topic. For an example, let’s take the Conference on College Composition and Communication’s statement “ Students’ Right to Their Own Language ,” which contains two annotated bibliographies. The second uses more recent sources and looks most like the annotated bibliographies you will write as a student, so let’s start there.

Example 3.8: Here are three annotations from that bibliography. As you read, take notice of the different highlighted colors. Phrases italicized and highlighted green identify ideas related to linguistic identity , phrases bolded and highlighted in blue identify concepts related to grammar analysis , and phrases underlined and highlighted orange identify groups and ideas related to educational objectives :

Fought, Carmen. Chicano English in Context. New York: Palgrave Macmillan, 2003.

Based primarily on data collected from adolescent and young adult native speakers in Los Angeles , this book is a comprehensive sociolinguistic study of language and language change in Latino/a communities. It provides the basics of Chicano English (CE) structure (phonology, syntax, and semantics) and its connection to the social and cultural identity of its speakers, along with detailed analyses of particular sociolinguistic variables. Emphasis is given to the historical, social, and linguistic contexts of CE. In addition, the differences between native and non-native CE speakers are covered. A final chapter discusses the future of research on CE.

Lippi-Green, Rosina. English with an Accent: Language, Ideology, and Discrimination in the United States . London and New York: Routledge, 1997.

The author examines linguistic facts about the structure and function of language , explores commonly held myths about language, and develops a model of “the language subordination process.” Then, using a case-study approach, she applies the model to specific institutional practices (e.g., in education, news media, business) to show how false assumptions about language lead to language subordination. The author analyzes specific groups and individuals (speakers of African American English, Southern U.S. English, and the foreign-language accent of Latinos and Asian Americans) and discusses why and how some embrace linguistic assimilation while others resist it.

Nero, Shondel J. Englishes in Contact: Anglophone Caribbean Students in an Urban College. Cresskill, NJ: Hampton Press, 2001.

This qualitative study of four anglophone Caribbean students at a New York City college offers an in-depth examination of the students’ written and spoken language and the challenges faced by both students and teachers as such students acquire academic literacy. Case studies of the four participants include excerpts from tape-recorded interviews, which reflect their linguistic self-perception, and sociolinguistic and educational experiences in their home countries and in New York City. Samples of their college writing over four semesters are represented and analyzed on morphosyntactic and discourse levels to determine the patterns that emerge when Creole English speakers attempt to write Standard Written English. Related issues such as language and identity , language attitudes, and educational responses to ethnolinguistic diversity are also discussed.

Once you have identified a concept like “language and identity” for your literature review, you can start getting “intertextual”! Review your other annotated sources and your new sources for their discussion of language and identity, as well as parallel concepts—what else do researchers address when they discuss language and identity? What do they discuss instead? Go back to the methods you used to come up with key terms for your literature search—the same strategies now apply to your reading. Also look for “umbrella” concepts, patterns in methodologies—anything that emerges while you read intertextually, focusing on the text in front of you while also remembering all the others you read before. Look for the themes in your annotated bibliography and keep track of the page numbers where these themes appear—plan to go back to those pages several times as you write your literature review.

This is a different type of reading than you did for the annotated bibliography, and might mean you go back and reread your sources several times in this new way—don’t think of this as just repeating labor you have already performed. This is new work, designed to uncover new things in the research. Re-reading articles multiple times is something all serious writers do, and something you should do, too. It isn’t redundant, it is recur sive .

Table 3.3: Synthesis Matrix for Individuals’ Choices in Linguistic Identity

Put your sources into conversations around your themes, as shown in the table above. Notice that the top row names the themes covered in that column, put into original wording similar, but not identical, to the wording in the annotated bibliographies. Not every source will address every topic—not every article is the same. The last row starts to describe what is happening in each column across the whole collection of texts. In this way, your synthesis matrix takes the ingredient list provided by the annotated bibliography and makes it into a recipe for your final product—the literature review.

More Resources 3.4: Synthesis Matrix

VI. Writing Strategies: Citation, Quotation, and Paraphrase

Citation is when you use the work of other authors in your writing and mark that portion of your writing so your reader understands what idea is being “borrowed.” Citation also tells your reader where they could find that original idea in the original text, and how your text fits together with the web of other texts related to your topic: in other words, citations help create intertextuality. A citation placed in your sentences should refer directly to the full bibliographic information in your Works Cited or References page.

As you read in Chapter 1, there are different styles of citation including AMA, APA, CMS, and MLA. You can refer back to that chapter for a more detailed explanation of each. In this section, we’ll cover the basics that are common to citation practices. Most academic styles use the original author’s last name as the central part of the in-text citation, since References pages usually list cited works alphabetically by last name, but some use footnotes or endnotes instead, listing works in the order they were cited. It is important to know which academic style you are using for your literature review so that you can make the right choice.

In-text citation takes one of two forms: parenthetical or narrative. In a narrative citation the author of the original work is mentioned in the sentence.

Example 3.9: Here’s an example taken from the introduction of the same literature review discussed in the Research Strategies: Developing a Methodology section of this chapter.

Several pieces offered a comprehensive review of the historical literature on the formation of Black English as a construct in the context of slavery and Jim Crow, and the historical teaching of Black English within the U .S. context, including Wheeler ( 2016 ) and Alim and Baugh (2007). Wheeler (2016) equated Standard English with ‘White’ English and challenged its hegemony in dialectically diverse classrooms. She named the “racism inherent in [fostering] bidialectalism [th rough teaching]” (p. 380), arguing that we are acknowledging that the only way for African-Americans to be upwardly mobile was to learn how to speak ‘White’ English. Alim (2010) , explained, “By uncritically presenting language varieties as ‘equal’ but diff ering in levels of ‘appropriateness,’ language and Dialect Awareness programs run the risk of silently legitimizing ‘Standard English’” (p. 215)…. Current work addressing AAVE studies has been shifting focus to translingualism and to promoting such pedag ogies as code-meshing (Young, Barrett, Young Rivera and Lovejoy, 2014) and translanguaging (García & Wei, García and Wei, 2014) , embedded in a critical analysis of the racial logics underpinning the denigration of some languages. This work, combined with e xtensive examinations of the connections between race, language, teaching, and identity ( e.g. Flores & Rosa, 2015; Alim et al., 2016 ), has laid a foundation for a raciolinguistics approach to teaching, which we return to later in this article. (Von Esch et al., 2020, p. 399, emphasis added .)

In the first sentence, we see two narrative citations just before the period. These citations state the authors’ names as a part of the sentence, and put the publication date of the articles in parenthesis. It makes sense to use a narrative citation in the topic sentence, since most of the paragraph is a synthesis of Wheeler and Alim’s research. The second sentence starts with Wheeler’s name in the subject position, and the fourth sentence starts with Alim’s name in the subject position—both are narrative citations, a form chosen by the author to emphasize the importance and similarities in the two articles.

In the last two sentences, we see parenthetical citations. The citation information is in parenthesis within the sentences, which focuses the reader on the ideas, not the research itself. Imagine you were reading this article out loud—you would most certainly say the narrative citations “Wheeler” and “Alim”; you might choose not to say “Young, Barrett, Young-Rivera, & Lovejoy, 2014,” though, and no one listening to you would notice the omission. This is the most important difference between narrative and parenthetical citation—narrative draws attention to the researchers, while parenthetical allows a focus on ideas. In academic writing, you often have reason to use both, but it is important to note that using parenthetical citation is less disruptive to your voice—it keeps a reader focused on the ideas you are explaining.

Usually you are citing a type of quotation in your text (although different disciplines have other situations that they cite). Direct quotation and paraphrase are usually what we talk about when we talk about using resources in your writing, although summary is cited as well.

Direct quotation is when you take the original words of one author and place them in your own text. When you quote in your own writing, you mark the copied text—usually with quotation marks “” around the text and a citation afterwards. Quoting is useful when the original author is an important authority on a topic or if you want to define/describe another’s point of view in a way that leaves no room for misinterpretation.

In a literature review, a direct quote will almost always be accompanied by a narrative citation. But direct quoting can cause some issues in your own text, such as a sudden shift in voice and a loss of cohesion; the potential for misunderstanding and misrepresentation, since the quote has been separated from its original context; and wordiness —quotes can take up too much space both in terms of the quote itself, and of the explanation and context you must provide for the introduced idea. For these reasons, literature reviews do not contain much direct quoting.

Paraphrasing is a way to accomplish similar goals to direct quoting without causing the same problems. Paraphrasing is when you use only the original author’s key terms and ideas, but your own words. Paraphrasing still contains a citation afterwards that directs the reader to the full bibliographic information in your Works Cited, but does not require quotation marks since the language is yours. Paraphrase may be longer or shorter than the original author’s text, and uses both narrative and parenthetical citation. Paraphrase also allows you to cite more than one piece of research containing the same idea in a single sentence, such as the last sentence in the example paragraph above. This kind of citation string is important to literature reviews because it clearly identifies patterns and trends in research findings.

Key Takeaways

• Literature reviews are a synthesis of what other researchers have discovered on your topic. Think of reviews as “the big picture.”
• Taking so much information from other sources can get confusing–use section headings to keep your review organized and clear.
• Diverse citation, quotation, and paraphrasing techniques are necessary to help your reader understand where the ideas are coming from, AND to help make the ideas “stick together.”
• Keeping all the new knowledge you are learning from your sources organized is hard! Take notes using citations and use a graphic organizer to keep yourself on track.

Fernandez, Lord, H., Halcomb, E., Moxham, L., Middleton, R., Alananzeh, I., & Ellwood, L. (2020). Implications for COVID-19: A systematic review of nurses’ experiences of working in acute care hospital settings during a respiratory pandemic. International Journal of Nursing Studies , 111. https://doi.org/10.1016/j.ijnurstu.2020.103637

Kassin, S. M., & Gudjonsson, G. H. (2004). The psychology of confessions. Psychological Science in the Public Interest , 5 (2), 33–67. https://doi.org/10.1111/j.1529-1006.2004.00016.x

National Council of Teachers of English. (2018, June 16). Students’ right to their own language (with bibliography) . Conference on College Composition and Communication. Retrieved July 24, 2022, from https://cccc.ncte.org/cccc/resources/positions/srtolsummary

NEIU Libraries. (2020). “How should I search in a database?”  YouTube . https://www.youtube.com/watch?v=8fgBF0EuH_o

Ratcliffe, E. (2021). Summary Flowchart [Image]. Frontiers in Psychology. https://www.frontiersin.org/articles/10.3389/fpsyg.2021.570563/full#B3

Ratcliffe, E. (2021). Sound and soundscape in restorative natural environments: A narrative literature review. Frontiers in Psychology , 12 . https://doi.org/10.3389/fpsyg.2021.570563

Sasaki. K. (2022). Synthesis and Recipes [Image].

Von Esch, K., Motha, S., & Kubota, R. (2020). Race and language teaching. Language Teaching, 53 (4), 391-421. doi:10.1017/S0261444820000269

Writing for Inquiry and Research Copyright © 2023 by Charitianne Williams is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Writing a Literature Review

• What is a Literature Review?
• Step 1: Choosing a Topic
• Step 2: Finding Information
• Step 3: Evaluating Content
• Step 4: Taking Notes
• Step 5: Synthesizing Content
• Step 6: Writing the Review
• Step 7: Citing Your Sources
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• Off-Campus & Mobile Access
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Writing the Review

You've done the research and now your ready to put your findings down on paper. When preparing to write your review, first consider how will you organize your review.

The actual review generally has 5 components:

• Introduction
• Bibliography

A good literature review shows signs of synthesis and understanding of the topic. There should be strong evidence of analytical thinking as illustrated through the connections you make between the literature being reviewed. Think of it this way- a literature review is much more than a book review. It is a document where you present your sources and their overall relationship to your thesis statement.

Conversly, a poor literature review will simply list and identify the sources . In essence, it will appear to be a glorifed annotated bibliography.

• Literature Reviews: The University of North Carolina http://writingcenter.unc.edu/handouts/literature-reviews/
• Writing a Literature Review: Wesleyan University
• Literature Review Tip Sheet: Edith Cowan University See additional information, including other tip sheets at http://intranet.ecu.edu.au/research/for-research-students/research-journey/designing-and-undertaking-your-research/reviewing-the-literature http://intranet.ecu.edu.au/student/my-studies/study-advice/academic-tip-sheets

The Abstract

An abstract is a summary of your literature review. It is made up of the following parts:

• A contextual sentence about your motivation behind your research topic
• Your thesis statement
• A descriptive statement about the types of literature used in the review
• Summarize your findings
• Conclusion(s) based upon your findings

The Introduction

Like a typical research paper introduction, provide the reader with a quick idea of the topic of the literature review:

• Define or identify the general topic, issue, or area of concern. This provides the reader with context for reviewing the literature.
• Point out overall trends in what has been published about the topic; or conflicts in theory, methodology, evidence, and conclusions; or gaps in research and scholarship; or a single problem or new perspective of immediate interest.
• Establish the your reason (point of view) for reviewing the literature; explain the criteria to be used in analyzing and comparing literature and the organization of the review (sequence); and, when necessary, state why certain literature is or is not included (scope).

The body of a literature review contains your discussion of sources and can be organized in 3 ways-

• Chronological - by publication or by trend
• Thematic - organized around a topic or issue, rather than the progression of time
• Methodical - the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the "methods" of the literture's researcher or writer that you are reviewing

You may also want to include a section on "questions for further research" and discuss what questions the review has sparked about the topic/field or offer suggestions for future studies/examinations that build on your current findings.

The Conclusion

In the conclusion, you should:

Conclude by providing some insight into the relationship between the central topic of the literature review and a larger area of study such as a discipline, a scientific endeavor, or a profession

The Bibliography

Since a literature review is composed of pieces of research, it is very important that your correctly cite the literature you are reviewing, both in the reviews body as well as in a bibliography/works cited. To learn more about different citation styles, visit the " Citing Your Sources " tab.

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Conducting a Literature Review

• Getting Started
• Define your Research Question
• Finding Sources
• Evaluating Sources
• Organizing the Review
• Cite and Manage your Sources

Introduction

Once you have your literature review planned out, you are ready to begin writing! Good organization and a clear focus are key to writing a successful academic paper of any kind, which is why the previous steps in this guide are so important; the more thorough you are with each of the preceding elements of writing the literature review, the easier this final step will be.

A literature review is organized into an introduction, multiple body paragraphs, and a conclusion. This format should be familiar to you, as it is the general outline of most academic essays; what is new and exciting about this literature review is the information you've gathered in your research and synthesized in your organization and outlining process.

Remember, if you ever need help with writing an essay of any kind, the ACPHS Writing Center is here to help! You can book an appointment with one of the peer tutors or reach out by email. The Library is also here to provide assistance with your assignments, particularly finding or citing resources.

Additional Resources

• Write a Literature Review by the University of Guelph McLaughlin Library

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Intro Paragraph & Thesis

Introductory paragraphs can be the most challenging part of writing a paper. Instead of laying out the evidence (or in the case of a literature review, analyzing your resources), you must first provide background information and context for the topic, discuss the body of literature in general as well as the scope of your review, and give a brief outline of how you will organize the review.

It is generally a good idea to open an introduction with a hook, or an interesting first sentence. This could be a statistic or fact about the topic that you find relevant, a rhetorical question that will be answered in the rest of the introduction, or even an appropriate anecdote. The point of a strong hook is to catch the reader's attention; for a literature review, it can help get the reader invested in the research around your topic, as well as your analysis of it.

Some authors prefer to write their introductory paragraph after completing the body of the essay, finding it easier to summarize what will be shared with the reader after it has already been written. There is no right or wrong order for crafting your paper, so if this method appeals to you then you should make use of it. However, with appropriately detailed planning it can be simple to write out an introduction prior to the body. Using an outline  (using the methods provided by Walden University, for example) can make writing the introduction and the entire essay much simpler.

Your literature review's introduction should contain four major elements:

• Establishing the topic, including providing background information and any necessary definitions to make sure your reader has all the context necessary to understand the rest of the literature review
• The trends or themes of the research that you noticed while compiling your sources, including any that you will use to organize your literature
• The purpose, criteria, and scope of the literature review: how will the literature be organized? What is your reason for examining this topic? What will you be analyzing about the sources (comparing/contrasting research methodology, conclusions, etc.)? Is there any literature you decided not to include -- if so, what disqualified it from the review?
• Introduce your thesis statement by drawing on the previous 3 components of the introduction to state what you discovered about the literature on this topic. Specifically, the thesis should answer where the current literature's strengths and weaknesses lie, and where additional research may be needed

The purpose of the introduction is to make sure that your reader has all the information they need to understand and appreciate your literature review, and to provide them a general blueprint of the analysis and arguments you will be making.

• 5 Questions to Strengthen Your Thesis Statement by the University of Guelph Digital Learning Commons

Body Paragraphs

With the introduction out of the way -- or perhaps even before you've written the introduction -- it's time to examine the literature you've gathered. We established how to organize the literature in the previous section of this guide, and that organization will serve as the framework for the body paragraphs. For example, if you organized your literature into themes, then each theme would serve as its own paragraph, in which you'd compare and contrast the sources within each theme; if you organized it by methodology or historical era, each of those would be a body paragraph.

As you write your literature analyses, keep the following recommendations in mind, provided by Shona McCombes at Scribbr :

Summarize  and synthesize:  give an overview of the main points of each source and combine them into a coherent whole Analyze and interpret:  don’t just  paraphrase  other researchers—add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole Critically evaluate:  mention the strengths and weaknesses of your sources Write in well-structured paragraphs:  use  transition words  and  topic sentences  to draw connections, comparisons and contrasts

Your summary of each source can be as detailed as is appropriate, based on how important the source is to the overall literature or how much analysis you have to perform on it. In general, the more significant a source is to your review, the more time should be devoted to summarizing and analyzing it.

While looking at individual sources, remember to keep connecting them back to the theme of the body paragraph and the overall thesis; explaining their relevance in a particular section of literature helps the reader follow along and better understand your overall arguments.

Other useful tips to keep in mind when writing your body paragraphs, provided by the Writing Center of the University of North Carolina at Chapel Hill :

• Use evidence to support your claims
• Be selective, and focus on the most important points for each piece of literature rather than trying to describe everything
• Use quotes when appropriate, but know that literature reviews do not frequently require direct quotations
• Paraphrase accurately
• Literature Reviews by the University of North Carolina at Chapel Hill's Writing Center

Conclusion & Reviewing Your Paper

Concluding Paragraph

A conclusion is used to provide further reinforcement of the arguments presented throughout the paper. In general, this consists of briefly summarizing the body paragraphs and reasserting their connection to your thesis. This is also good practice for a literature review; in addition, your conclusion should again summarize the broad trends of the research on your topic, as well as any opportunities for additional or more thorough research that you've found. 

Below are some helpful recommendations for writing conclusions, compiled from advice explained in more detail in the links below:

• Address the broader implications of the existing research, and why it is important to close the gaps you evaluated during your literature review
• Include a quotation or fact that effectively illustrates your thesis in a provocative or interesting way
• Use simple, clear language without jargon
• Reestablish your thesis and its connection with the literature reviewed

Your goal with the concluding paragraph of your literature review should be to leave the reader with a firm understanding of the existing literature on your topic, where additional research may be necessary, and why it matters.

Revising Your Literature Review

Revision is a process that goes beyond simply correcting spelling and grammar mistakes -- though proofreading is an important part of the writing process as well. The purpose of revising your literature review before submission is to look at it the way your reader will and pick up on any potential leaps of logic, unclear explanations, or shoddy evidence. The revision process should not begin immediately after finishing the paper; whenever possible, wait a few hours or days before looking at your draft, so that you can approach it with fresh eyes. 

When revising, focus on major issues with the paper such as organization, clarity, and thoroughness. Trying to both revise your writing and proofread it for small spelling or grammar issues may distract you from more important areas that could be improved. Ask yourself if your thesis is well-defended by the body paragraphs, and if you still agree with the conclusions you stated in the introduction. If more or better arguments are needed, find places in the body paragraphs to add evidence or make clearer connections to your thesis. Focus on the flow of the review; does each body paragraph move naturally into the next one? Do your paragraphs need to be reordered or restructured?

After major revisions are done, it is time to proofread for spelling, grammar, and general writing errors. Try reading the paper out loud and seeing where your word choice could be strengthened or a run-on sentence could be amended.

It can sometimes be difficult to revise an essay on your own, so consider booking an appointment with the ACPHS Writing Center to go over your writing with a tutor. Friends, classmates, or your professor can also be useful sources of feedback, and if possible try to get as many different readers to look over your writing and provide insight.

• Revising Drafts by the University of North Carolina at Chapel Hill Writing Center
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Literature Reviews

• "How To" Books
• Examples of Literature Reviews
• Collecting Resources for a Literature Review
• Organizing the Literature Review
• Writing the Literature Review
• Endnote This link opens in a new window
• Evaluating Websites

Organization

Organization of your Literature Review

What is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? What order should you present them?

Just like most academic papers, literature reviews must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper.

Introduction: Gives a quick idea of the topic of the literature review, such as the central theme or organizational pattern.

Body: Contains your discussion of sources and is organized either chronologically, thematically, or methodologically (see below for more information on each).

Conclusions/Recommendations: Discuss what you have drawn from reviewing the literature so far. Where might the discussion proceed?

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario and then three typical ways of organizing the sources into a review:

You've decided to focus your literature review on materials dealing with sperm whales. This is because you've just finished reading Moby Dick, and you wonder if that whale's portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980's. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Chronological

If your review follows the chronological method, you could write about the materials above according to when they were published. For instance, first you would talk about the British biological studies of the 18th century, then about Moby Dick, published in 1851, then the book on sperm whales in other art (1968), and finally the biology articles (1980s) and the recent articles on American whaling of the 19th century. But there is relatively no continuity among subjects here. And notice that even though the sources on sperm whales in other art and on American whaling are written recently, they are about other subjects/objects that were created much earlier. Thus, the review loses its chronological focus.

By publication

Order your sources chronologically by publication if the order demonstrates a more important trend. For instance, you could order a review of literature on biological studies of sperm whales if the progression revealed a change in dissection practices of the researchers who wrote and/or conducted the studies.

Another way to organize sources chronologically is to examine the sources under a trend, such as the history of whaling. Then your review would have subsections according to eras within this period. For instance, the review might examine whaling from pre-1600-1699, 1700-1799, and 1800-1899. Using this method, you would combine the recent studies on American whaling in the 19th century with Moby Dick itself in the 1800-1899 category, even though the authors wrote a century apart.

Thematic reviews of literature are organized around a topic or issue, rather than the progression of time. However, progression of time may still be an important factor in a thematic review. For instance, the sperm whale review could focus on the development of the harpoon for whale hunting. While the study focuses on one topic, harpoon technology, it will still be organized chronologically. The only difference here between a "chronological" and a "thematic" approach is what is emphasized the most: the development of the harpoon or the harpoon technology.

More authentic thematic reviews tend to break away from chronological order. For instance, a thematic review of material on sperm whales might examine how they are portrayed as "evil" in cultural documents. The subsections might include how they are personified, how their proportions are exaggerated, and their behaviors misunderstood. A review organized in this manner would shift between time periods within each section according to the point made.

Methodological

A methodological approach differs from the two above in that the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the "methods" of the researcher or writer. For the sperm whale project, one methodological approach would be to look at cultural differences between the portrayal of whales in American, British, and French art work. Or the review might focus on the economic impact of whaling on a community. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Once you've decided on the organizational method for the body of the review, the sections you need to include in the paper should be easy to figure out. They should arise out of your organizational strategy. In other words, a chronological review would have subsections for each vital time period. A thematic review would have subtopics based upon factors that relate to the theme or issue.

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

Current Situation: Information necessary to understand the topic or focus of the literature review.

History: The chronological progression of the field, the literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.

Methods and/or Standards: The criteria you used to select the sources in your literature review or the way in which you present your information. For instance, you might explain that your review includes only peer-reviewed articles and journals.

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

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How to Write a Literature Review

As every student knows, writing informative essay and research papers is an integral part of the educational program. You create a thesis, support it using valid sources, and formulate systematic ideas surrounding it. However, not all students know that they will also have to face another type of paper known as a Literature Review in college. Let's take a closer look at this with our custom essay writer .

Literature Review Definition

As this is a less common academic writing type, students often ask: "What is a literature review?" According to the definition, a literature review is a body of work that explores various publications within a specific subject area and sometimes within a set timeframe.

This type of writing requires you to read and analyze various sources that relate to the main subject and present each unique comprehension of the publications. Lastly, a literature review should combine a summary with a synthesis of the documents used. A summary is a brief overview of the important information in the publication; a synthesis is a re-organization of the information that gives the writing a new and unique meaning.

Typically, a literature review is a part of a larger paper, such as a thesis or dissertation. However, you may also be given it as a stand-alone assignment.

The Purpose

The main purpose of a literature review is to summarize and synthesize the ideas created by previous authors without implementing personal opinions or other additional information.

However, a literature review objective is not just to list summaries of sources; rather, it is to notice a central trend or principle in all of the publications. Just like a research paper has a thesis that guides it on rails, a literature review has the main organizing principle (MOP). The goal of this type of academic writing is to identify the MOP and show how it exists in all of your supporting documents.

Why is a literature review important? The value of such work is explained by the following goals it pursues:

• Highlights the significance of the main topic within a specific subject area.
• Demonstrates and explains the background of research for a particular subject matter.
• Helps to find out the key themes, principles, concepts, and researchers that exist within a topic.
• Helps to reveal relationships between existing ideas/studies on a topic.
• Reveals the main points of controversy and gaps within a topic.
• Suggests questions to drive primary research based on previous studies.

Here are some example topics for writing literature reviews:

• Exploring racism in "To Kill a Mockingbird," "The Adventures of Huckleberry Finn," and "Uncle Tom's Cabin."
• Isolationism in "The Catcher in the Rye," "Frankenstein," and "1984"
• Understanding Moral Dilemmas in "Crime and Punishment," "The Scarlet Letter," and "The Lifeboat"
• Corruption of Power in "Macbeth," "All the King's Men," and "Animal Farm"
• Emotional and Physical survival in "Lord of the Flies," "Hatchet," and "Congo."

How Long Is a Literature Review?

When facing the need to write a literature review, students tend to wonder, "how long should a literature review be?" In some cases, the length of your paper's body may be determined by your instructor. Be sure to read the guidelines carefully to learn what is expected from you.

Keeping your literature review around 15-30% of your entire paper is recommended if you haven't been provided with specific guidelines. To give you a rough idea, that is about 2-3 pages for a 15-page paper. In case you are writing a literature review as a stand-alone assignment, its length should be specified in the instructions provided.

Literature Review Format: APA, MLA, and Chicago

The essay format you use should adhere to the citation style preferred by your instructor. Seek clarification from your instructor for several other components as well to establish a desired literature review format:

• How many sources should you review, and what kind of sources should they be (published materials, journal articles, or websites)?
• What format should you use to cite the sources?
• How long should the review be?
• Should your review consist of a summary, synthesis, or a personal critique?
• Should your review include subheadings or background information for your sources?

If you want to format your paper in APA style, then follow these rules:

• Use 1-inch page margins.
• Unless provided with other instructions, use double-spacing throughout the whole text.
• Make sure you choose a readable font. The preferred font for APA papers is Times New Roman set to 12-point size.
• Include a header at the top of every page (in capital letters). The page header must be a shortened version of your essay title and limited to 50 characters, including spacing and punctuation.
• Put page numbers in the upper right corner of every page.
• When shaping your literature review outline in APA, don't forget to include a title page. This page should include the paper's name, the author's name, and the institutional affiliation. Your title must be typed with upper and lowercase letters and centered in the upper part of the page; use no more than 12 words, and avoid using abbreviations and useless words.

For MLA style text, apply the following guidelines:

• Double your spacing across the entire paper.
• Set ½-inch indents for each new paragraph.
• The preferred font for MLA papers is Times New Roman set to 12-point size.
• Include a header at the top of your paper's first page or on the title page (note that MLA style does not require you to have a title page, but you are allowed to decide to include one). A header in this format should include your full name; the name of your instructor; the name of the class, course, or section number; and the due date of the assignment.
• Include a running head in the top right corner of each page in your paper. Place it one inch from the page's right margin and half an inch from the top margin. Only include your last name and the page number separated by a space in the running head. Do not put the abbreviation p. before page numbers.

Finally, if you are required to write a literature review in Chicago style, here are the key rules to follow:

• Set page margins to no less than 1 inch.
• Use double spacing across the entire text, except when it comes to table titles, figure captions, notes, blockquotes, and entries within the bibliography or References.
• Do not put spaces between paragraphs.
• Make sure you choose a clear and easily-readable font. The preferred fonts for Chicago papers are Times New Roman and Courier, set to no less than 10-point size, but preferably to 12-point size.
• A cover (title) page should include your full name, class information, and the date. Center the cover page and place it one-third below the top of the page.
• Place page numbers in the upper right corner of each page, including the cover page.

Read also about harvard format - popular style used in papers.

Structure of a Literature Review

How to structure a literature review: Like many other types of academic writing, a literature review follows a typical intro-body-conclusion style with 5 paragraphs overall. Now, let’s look at each component of the basic literature review structure in detail:

• Introduction

You should direct your reader(s) towards the MOP (main organizing principle). This means that your information must start from a broad perspective and gradually narrow down until it reaches your focal point.

Start by presenting your general concept (Corruption, for example). After the initial presentation, narrow your introduction's focus towards the MOP by mentioning the criteria you used to select the literature sources you have chosen (Macbeth, All the King's Men, and Animal Farm). Finally, the introduction will end with the presentation of your MOP that should directly link it to all three literature sources.

Body Paragraphs

Generally, each body paragraph will focus on a specific source of literature laid out in the essay's introduction. As each source has its own frame of reference for the MOP, it is crucial to structure the review in the most logically consistent way possible. This means the writing should be structured chronologically, thematically or methodologically.

Chronologically

Breaking down your sources based on their publication date is a solid way to keep a correct historical timeline. If applied properly, it can present the development of a certain concept over time and provide examples in the form of literature. However, sometimes there are better alternatives we can use to structure the body.

Thematically

Instead of taking the "timeline approach," another option can be looking at the link between your MOP and your sources. Sometimes, the main idea will just glare from a piece of literature. Other times, the author may have to seek examples to prove their point. An experienced writer will usually present their sources by order of strength. For example, in "To Kill A Mockingbird," the entire novel was centralized around racism; in "The Adventures of Huckleberry Finn," racism was one of many themes.

Methodologically

As made obvious by the terminology, this type of structuring focuses on the methods used to present the central concept. For example, in "1984", George Orwell uses the law-and-order approach and shows the dangers of a dystopia for a social species.

In "Frankenstein," Mary Shelley exposes the character's physical traits as repulsive and horrifying, forcing him to suffer in an isolated environment. By showcasing the various methods used to portray the MOP, the writer can compare them based on things like severity, ethicality, and overall impact.

After presenting your key findings in the body paragraphs, there are 3 final objectives to complete in the essay's conclusion. First, the author should summarize the findings they have made or found, in other words, and briefly answer the question: "What have you learned?"

After discussing that information, the next step is to present the significance of the information about our current world today. In other words, how can the reader take the information and apply it to today's society? From that point, we finish off with a breadcrumb trail.

As the author, you want to leave the readers' trail of thought within the actual essay topic. This provides them with a means of further investigation—meaning that the reader may consider where the discussion will go next.

Writing an Outline for a Literature Review

Students often underestimate the importance of planning the structure of their papers in advance. However, this is not a wise approach. Having a rough APA literature review outline (or other style outlines) will not only help you follow the right format and structure but will also make the writing process simpler and help ensure that you include all of the important information without missing anything.

How to write a literature review outline: As you already know from the Structure section of this guide, every part of your literature review performs its own important role. Therefore, you should create your outline while keeping the general introduction-body-conclusion structure in mind and ensuring that each section meets its own objectives. However, it is important to remember that a literature review outline is slightly different from outlines of other types of essays because it does not provide new information. Instead, it focuses on existing studies relevant to the main topic. ‍

Here is a literature review outline example on the subject of the Ebola virus to help you get it right:

• Introduce the general topic. Provide background information on the Ebola virus: genome, pathogenesis, transmission, epidemiology, treatment, etc.
• Shape the main research question: What is the potential role of arthropods (mechanical or biological vectors) in the distribution of the Ebola virus?
• Methodology: For example, the information was searched through X databases to find relevant research articles about the Ebola virus and arthropods' role in its spreading. The data was extracted using a standardized form.
• Expected outcomes
• Overall trends in the literature on this topic: While the natural reservoir of the virus is still not known with certainty, many researchers believe that arthropods (and fruit bats, in particular) pay a significant role in the distribution of the virus.
• Subject 1: A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Subject 2: A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Subject 3:  A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Indicate the relationships between the pieces of literature discussed. Emphasize key themes, common patterns, and trends. Talk about the pros and cons of the different approaches taken by the authors/researchers.
• State which studies seem to be the most influential.
• Emphasize the major contradictions and points of disagreement. Define the gaps still to be covered (if any).
• If applicable: define how your own study will contribute to further disclosure of the topic.

Hopefully, this sample outline will help you to structure your own paper. However, if you feel like you need some more advice on how to organize your review, don’t hesitate to search for more literature review outline examples in APA or other styles on the Web, or simply ask our writers to get a dissertation help .

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How to Write a Good Literature Review

Whether you are writing a literature review within the framework of a large research project (e.g. thesis, dissertation, or other) or as a stand-alone assignment, the approach you should take to writing generally remains the same.

Whether you are writing a literature review within the framework of a large research project (e.g., thesis, dissertation, or other) or as a stand-alone assignment, the approach you should take to writing generally remains the same.

Now, as you know about the general rules and have a basic literature review outline template, let's define the steps to take to handle this task right with our service:

Step 1: Identifying the Topic

This is probably the only matter you may approach differently depending on whether your literature review comes within a research paper or a separate assignment altogether. If you are creating a literature review as a part of another work, you need to search for literature related to your main research questions and problems. Respectively, if you are writing it as a stand-alone task, you will have to pick a relevant topic and central question upon which you will collect the literature. Earlier in this guide, we suggested some engaging topics to guide your search.

Step 2: Conducting Research

When you have a clearly defined topic, it is time to start collecting literature for your review. We recommend starting by compiling a list of relevant keywords related to your central question—to make the entire research process much simpler and help you find relevant publications faster.

When you have a list of keywords, use them to search for valid and relevant sources. At this point, be sure to use only trusted sources, such as ones from university libraries, online scientific databases, etc.

Once you have found some sources, be sure to define whether or not they are actually relevant to your topic and research question. To save time, you can read abstracts to get general ideas of what the papers are about instead of the whole thing.

Pro Tip: When you finally find a few valid publications, take a look at their bibliographies to discover other relevant sources as well.

Step 3: Assess and Prioritize Sources

Throughout your research, you will likely find plenty of relevant literature to include in your literature review. At this point, students often make the mistake of trying to fit all the collected sources into their reviews. Instead, we suggest looking at what you've collected once more, evaluating the available sources, and selecting the most relevant ones. You most likely won't be able to read everything you find on a given topic and then be able to synthesize all of the sources into a single literature review. That's why prioritizing them is important.

To evaluate which sources are worth including in your review, keep in mind the following criteria:

• Credibility;
• Innovation;
• Key insights;

Furthermore, as you read the sources, don’t forget to take notes on everything you can incorporate into the review later. And be sure to get your citations in place early on. If you cite the selected sources at the initial stage, you will find it easier to create your annotated bibliography later on.

Step 4: Identify Relationships, Key Ideas, and Gaps

Before you can move on to outlining and writing your literature review, the final step is determining the relationships between the studies that already exist. Identifying the relationships will help you organize the existing knowledge, build a solid literature outline, and (if necessary) indicate your own research contribution to a specific field.

Some of the key points to keep an eye out for are:

• Main themes;
• Contradictions and debates;
• Influential studies or theories;
• Trends and patterns;

Here are a few examples: Common trends may include a focus on specific groups of people across different studies. Most researchers may have increased interest in certain aspects of the topic regarding key themes. Contradictions may include some disagreement concerning the theories and outcomes of a study. And finally, gaps most often refer to a lack of research on certain aspects of a topic.

Step 5: Make an Outline

Although students tend to neglect this stage, outlining is one of the most important steps in writing every academic paper. This is the easiest way to organize the body of your text and ensure that you haven't missed anything important. Besides, having a rough idea of what you will write about in the paper will help you get it right faster and more easily. Earlier in this guide, we already discussed the basic structure of a literature review and gave you an example of a good outline. At this workflow stage, you can use all of the knowledge you've gained from us to build your own outline.

Step 6: Move on to Writing

Having found and created all of your sources, notes, citations, and a detailed outline, you can finally get to the writing part of the process. At this stage, all you need to do is follow the plan you've created and keep in mind the overall structure and format defined in your professor's instructions.

Step 7: Adding the Final Touches

Most students make a common mistake and skip the final stage of the process, which includes proofreading and editing. We recommend taking enough time for these steps to ensure that your work will be worth the highest score. Do not underestimate the importance of proofreading and editing, and allocate enough time for these steps.

Pro Tip: Before moving on to proofreading and editing, be sure to set your literature review aside for a day or two. This will give you a chance to take your mind off it and then get back to proofreading with a fresh perspective. This tip will ensure that you won't miss out on any gaps or errors that might be present in your text.

These steps will help you create a top-notch literature review with ease! Want to get more advice on how to handle this body of work? Here are the top 3 tips you need to keep in mind when writing a literature review:

1. Good Sources

When working on a literature review, the most important thing any writer should remember is to find the best possible sources for their MOP. This means that you should select and filter through about 5-10 different options while doing initial research.

The stronger a piece of literature showcases the central point, the better the quality of the entire review.

2. Synthesize The Literature

Make sure to structure the review in the most effective way possible, whether it be chronologically, thematically, or methodologically. Understand what exactly you would like to say, and structure the source comparison accordingly.

3. Avoid Generalizations

Remember that each piece of literature will approach the MOP from a different angle. As the author, make sure to present the contrasts in approaches clearly and don't include general statements that offer no value.

Literature Review Examples

You can find two well-written literature reviews by the EssayPro writing team below. They will help you understand what the final product of a literature review should ideally look like.

The first literature review compares monolingual and bilingual language acquisition skills and uses various sources to prove its point:

The second literature review compares the impact of fear and pain on a protagonist’s overall development in various settings:

Both reviews will help you sharpen your skills and provide good guidelines for writing high-quality papers.

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Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.

Handbook of eHealth Evaluation: An Evidence-based Approach [Internet].

Chapter 9 methods for literature reviews.

Guy Paré and Spyros Kitsiou .

9.1. Introduction

Literature reviews play a critical role in scholarship because science remains, first and foremost, a cumulative endeavour ( vom Brocke et al., 2009 ). As in any academic discipline, rigorous knowledge syntheses are becoming indispensable in keeping up with an exponentially growing eHealth literature, assisting practitioners, academics, and graduate students in finding, evaluating, and synthesizing the contents of many empirical and conceptual papers. Among other methods, literature reviews are essential for: (a) identifying what has been written on a subject or topic; (b) determining the extent to which a specific research area reveals any interpretable trends or patterns; (c) aggregating empirical findings related to a narrow research question to support evidence-based practice; (d) generating new frameworks and theories; and (e) identifying topics or questions requiring more investigation ( Paré, Trudel, Jaana, & Kitsiou, 2015 ).

Literature reviews can take two major forms. The most prevalent one is the “literature review” or “background” section within a journal paper or a chapter in a graduate thesis. This section synthesizes the extant literature and usually identifies the gaps in knowledge that the empirical study addresses ( Sylvester, Tate, & Johnstone, 2013 ). It may also provide a theoretical foundation for the proposed study, substantiate the presence of the research problem, justify the research as one that contributes something new to the cumulated knowledge, or validate the methods and approaches for the proposed study ( Hart, 1998 ; Levy & Ellis, 2006 ).

The second form of literature review, which is the focus of this chapter, constitutes an original and valuable work of research in and of itself ( Paré et al., 2015 ). Rather than providing a base for a researcher’s own work, it creates a solid starting point for all members of the community interested in a particular area or topic ( Mulrow, 1987 ). The so-called “review article” is a journal-length paper which has an overarching purpose to synthesize the literature in a field, without collecting or analyzing any primary data ( Green, Johnson, & Adams, 2006 ).

When appropriately conducted, review articles represent powerful information sources for practitioners looking for state-of-the art evidence to guide their decision-making and work practices ( Paré et al., 2015 ). Further, high-quality reviews become frequently cited pieces of work which researchers seek out as a first clear outline of the literature when undertaking empirical studies ( Cooper, 1988 ; Rowe, 2014 ). Scholars who track and gauge the impact of articles have found that review papers are cited and downloaded more often than any other type of published article ( Cronin, Ryan, & Coughlan, 2008 ; Montori, Wilczynski, Morgan, Haynes, & Hedges, 2003 ; Patsopoulos, Analatos, & Ioannidis, 2005 ). The reason for their popularity may be the fact that reading the review enables one to have an overview, if not a detailed knowledge of the area in question, as well as references to the most useful primary sources ( Cronin et al., 2008 ). Although they are not easy to conduct, the commitment to complete a review article provides a tremendous service to one’s academic community ( Paré et al., 2015 ; Petticrew & Roberts, 2006 ). Most, if not all, peer-reviewed journals in the fields of medical informatics publish review articles of some type.

The main objectives of this chapter are fourfold: (a) to provide an overview of the major steps and activities involved in conducting a stand-alone literature review; (b) to describe and contrast the different types of review articles that can contribute to the eHealth knowledge base; (c) to illustrate each review type with one or two examples from the eHealth literature; and (d) to provide a series of recommendations for prospective authors of review articles in this domain.

9.2. Overview of the Literature Review Process and Steps

As explained in Templier and Paré (2015) , there are six generic steps involved in conducting a review article:

• formulating the research question(s) and objective(s),
• searching the extant literature,
• screening for inclusion,
• assessing the quality of primary studies,
• extracting data, and
• analyzing data.

Although these steps are presented here in sequential order, one must keep in mind that the review process can be iterative and that many activities can be initiated during the planning stage and later refined during subsequent phases ( Finfgeld-Connett & Johnson, 2013 ; Kitchenham & Charters, 2007 ).

Formulating the research question(s) and objective(s): As a first step, members of the review team must appropriately justify the need for the review itself ( Petticrew & Roberts, 2006 ), identify the review’s main objective(s) ( Okoli & Schabram, 2010 ), and define the concepts or variables at the heart of their synthesis ( Cooper & Hedges, 2009 ; Webster & Watson, 2002 ). Importantly, they also need to articulate the research question(s) they propose to investigate ( Kitchenham & Charters, 2007 ). In this regard, we concur with Jesson, Matheson, and Lacey (2011) that clearly articulated research questions are key ingredients that guide the entire review methodology; they underscore the type of information that is needed, inform the search for and selection of relevant literature, and guide or orient the subsequent analysis. Searching the extant literature: The next step consists of searching the literature and making decisions about the suitability of material to be considered in the review ( Cooper, 1988 ). There exist three main coverage strategies. First, exhaustive coverage means an effort is made to be as comprehensive as possible in order to ensure that all relevant studies, published and unpublished, are included in the review and, thus, conclusions are based on this all-inclusive knowledge base. The second type of coverage consists of presenting materials that are representative of most other works in a given field or area. Often authors who adopt this strategy will search for relevant articles in a small number of top-tier journals in a field ( Paré et al., 2015 ). In the third strategy, the review team concentrates on prior works that have been central or pivotal to a particular topic. This may include empirical studies or conceptual papers that initiated a line of investigation, changed how problems or questions were framed, introduced new methods or concepts, or engendered important debate ( Cooper, 1988 ). Screening for inclusion: The following step consists of evaluating the applicability of the material identified in the preceding step ( Levy & Ellis, 2006 ; vom Brocke et al., 2009 ). Once a group of potential studies has been identified, members of the review team must screen them to determine their relevance ( Petticrew & Roberts, 2006 ). A set of predetermined rules provides a basis for including or excluding certain studies. This exercise requires a significant investment on the part of researchers, who must ensure enhanced objectivity and avoid biases or mistakes. As discussed later in this chapter, for certain types of reviews there must be at least two independent reviewers involved in the screening process and a procedure to resolve disagreements must also be in place ( Liberati et al., 2009 ; Shea et al., 2009 ). Assessing the quality of primary studies: In addition to screening material for inclusion, members of the review team may need to assess the scientific quality of the selected studies, that is, appraise the rigour of the research design and methods. Such formal assessment, which is usually conducted independently by at least two coders, helps members of the review team refine which studies to include in the final sample, determine whether or not the differences in quality may affect their conclusions, or guide how they analyze the data and interpret the findings ( Petticrew & Roberts, 2006 ). Ascribing quality scores to each primary study or considering through domain-based evaluations which study components have or have not been designed and executed appropriately makes it possible to reflect on the extent to which the selected study addresses possible biases and maximizes validity ( Shea et al., 2009 ). Extracting data: The following step involves gathering or extracting applicable information from each primary study included in the sample and deciding what is relevant to the problem of interest ( Cooper & Hedges, 2009 ). Indeed, the type of data that should be recorded mainly depends on the initial research questions ( Okoli & Schabram, 2010 ). However, important information may also be gathered about how, when, where and by whom the primary study was conducted, the research design and methods, or qualitative/quantitative results ( Cooper & Hedges, 2009 ). Analyzing and synthesizing data : As a final step, members of the review team must collate, summarize, aggregate, organize, and compare the evidence extracted from the included studies. The extracted data must be presented in a meaningful way that suggests a new contribution to the extant literature ( Jesson et al., 2011 ). Webster and Watson (2002) warn researchers that literature reviews should be much more than lists of papers and should provide a coherent lens to make sense of extant knowledge on a given topic. There exist several methods and techniques for synthesizing quantitative (e.g., frequency analysis, meta-analysis) and qualitative (e.g., grounded theory, narrative analysis, meta-ethnography) evidence ( Dixon-Woods, Agarwal, Jones, Young, & Sutton, 2005 ; Thomas & Harden, 2008 ).

9.3. Types of Review Articles and Brief Illustrations

EHealth researchers have at their disposal a number of approaches and methods for making sense out of existing literature, all with the purpose of casting current research findings into historical contexts or explaining contradictions that might exist among a set of primary research studies conducted on a particular topic. Our classification scheme is largely inspired from Paré and colleagues’ (2015) typology. Below we present and illustrate those review types that we feel are central to the growth and development of the eHealth domain.

9.3.1. Narrative Reviews

The narrative review is the “traditional” way of reviewing the extant literature and is skewed towards a qualitative interpretation of prior knowledge ( Sylvester et al., 2013 ). Put simply, a narrative review attempts to summarize or synthesize what has been written on a particular topic but does not seek generalization or cumulative knowledge from what is reviewed ( Davies, 2000 ; Green et al., 2006 ). Instead, the review team often undertakes the task of accumulating and synthesizing the literature to demonstrate the value of a particular point of view ( Baumeister & Leary, 1997 ). As such, reviewers may selectively ignore or limit the attention paid to certain studies in order to make a point. In this rather unsystematic approach, the selection of information from primary articles is subjective, lacks explicit criteria for inclusion and can lead to biased interpretations or inferences ( Green et al., 2006 ). There are several narrative reviews in the particular eHealth domain, as in all fields, which follow such an unstructured approach ( Silva et al., 2015 ; Paul et al., 2015 ).

Despite these criticisms, this type of review can be very useful in gathering together a volume of literature in a specific subject area and synthesizing it. As mentioned above, its primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research ( Cronin et al., 2008 ). Faculty like to use narrative reviews in the classroom because they are often more up to date than textbooks, provide a single source for students to reference, and expose students to peer-reviewed literature ( Green et al., 2006 ). For researchers, narrative reviews can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping researchers to determine research questions or formulate hypotheses. Importantly, narrative reviews can also be used as educational articles to bring practitioners up to date with certain topics of issues ( Green et al., 2006 ).

Recently, there have been several efforts to introduce more rigour in narrative reviews that will elucidate common pitfalls and bring changes into their publication standards. Information systems researchers, among others, have contributed to advancing knowledge on how to structure a “traditional” review. For instance, Levy and Ellis (2006) proposed a generic framework for conducting such reviews. Their model follows the systematic data processing approach comprised of three steps, namely: (a) literature search and screening; (b) data extraction and analysis; and (c) writing the literature review. They provide detailed and very helpful instructions on how to conduct each step of the review process. As another methodological contribution, vom Brocke et al. (2009) offered a series of guidelines for conducting literature reviews, with a particular focus on how to search and extract the relevant body of knowledge. Last, Bandara, Miskon, and Fielt (2011) proposed a structured, predefined and tool-supported method to identify primary studies within a feasible scope, extract relevant content from identified articles, synthesize and analyze the findings, and effectively write and present the results of the literature review. We highly recommend that prospective authors of narrative reviews consult these useful sources before embarking on their work.

Darlow and Wen (2015) provide a good example of a highly structured narrative review in the eHealth field. These authors synthesized published articles that describe the development process of mobile health ( m-health ) interventions for patients’ cancer care self-management. As in most narrative reviews, the scope of the research questions being investigated is broad: (a) how development of these systems are carried out; (b) which methods are used to investigate these systems; and (c) what conclusions can be drawn as a result of the development of these systems. To provide clear answers to these questions, a literature search was conducted on six electronic databases and Google Scholar . The search was performed using several terms and free text words, combining them in an appropriate manner. Four inclusion and three exclusion criteria were utilized during the screening process. Both authors independently reviewed each of the identified articles to determine eligibility and extract study information. A flow diagram shows the number of studies identified, screened, and included or excluded at each stage of study selection. In terms of contributions, this review provides a series of practical recommendations for m-health intervention development.

9.3.2. Descriptive or Mapping Reviews

The primary goal of a descriptive review is to determine the extent to which a body of knowledge in a particular research topic reveals any interpretable pattern or trend with respect to pre-existing propositions, theories, methodologies or findings ( King & He, 2005 ; Paré et al., 2015 ). In contrast with narrative reviews, descriptive reviews follow a systematic and transparent procedure, including searching, screening and classifying studies ( Petersen, Vakkalanka, & Kuzniarz, 2015 ). Indeed, structured search methods are used to form a representative sample of a larger group of published works ( Paré et al., 2015 ). Further, authors of descriptive reviews extract from each study certain characteristics of interest, such as publication year, research methods, data collection techniques, and direction or strength of research outcomes (e.g., positive, negative, or non-significant) in the form of frequency analysis to produce quantitative results ( Sylvester et al., 2013 ). In essence, each study included in a descriptive review is treated as the unit of analysis and the published literature as a whole provides a database from which the authors attempt to identify any interpretable trends or draw overall conclusions about the merits of existing conceptualizations, propositions, methods or findings ( Paré et al., 2015 ). In doing so, a descriptive review may claim that its findings represent the state of the art in a particular domain ( King & He, 2005 ).

In the fields of health sciences and medical informatics, reviews that focus on examining the range, nature and evolution of a topic area are described by Anderson, Allen, Peckham, and Goodwin (2008) as mapping reviews . Like descriptive reviews, the research questions are generic and usually relate to publication patterns and trends. There is no preconceived plan to systematically review all of the literature although this can be done. Instead, researchers often present studies that are representative of most works published in a particular area and they consider a specific time frame to be mapped.

An example of this approach in the eHealth domain is offered by DeShazo, Lavallie, and Wolf (2009). The purpose of this descriptive or mapping review was to characterize publication trends in the medical informatics literature over a 20-year period (1987 to 2006). To achieve this ambitious objective, the authors performed a bibliometric analysis of medical informatics citations indexed in medline using publication trends, journal frequencies, impact factors, Medical Subject Headings (MeSH) term frequencies, and characteristics of citations. Findings revealed that there were over 77,000 medical informatics articles published during the covered period in numerous journals and that the average annual growth rate was 12%. The MeSH term analysis also suggested a strong interdisciplinary trend. Finally, average impact scores increased over time with two notable growth periods. Overall, patterns in research outputs that seem to characterize the historic trends and current components of the field of medical informatics suggest it may be a maturing discipline (DeShazo et al., 2009).

9.3.3. Scoping Reviews

Scoping reviews attempt to provide an initial indication of the potential size and nature of the extant literature on an emergent topic (Arksey & O’Malley, 2005; Daudt, van Mossel, & Scott, 2013 ; Levac, Colquhoun, & O’Brien, 2010). A scoping review may be conducted to examine the extent, range and nature of research activities in a particular area, determine the value of undertaking a full systematic review (discussed next), or identify research gaps in the extant literature ( Paré et al., 2015 ). In line with their main objective, scoping reviews usually conclude with the presentation of a detailed research agenda for future works along with potential implications for both practice and research.

Unlike narrative and descriptive reviews, the whole point of scoping the field is to be as comprehensive as possible, including grey literature (Arksey & O’Malley, 2005). Inclusion and exclusion criteria must be established to help researchers eliminate studies that are not aligned with the research questions. It is also recommended that at least two independent coders review abstracts yielded from the search strategy and then the full articles for study selection ( Daudt et al., 2013 ). The synthesized evidence from content or thematic analysis is relatively easy to present in tabular form (Arksey & O’Malley, 2005; Thomas & Harden, 2008 ).

One of the most highly cited scoping reviews in the eHealth domain was published by Archer, Fevrier-Thomas, Lokker, McKibbon, and Straus (2011) . These authors reviewed the existing literature on personal health record ( phr ) systems including design, functionality, implementation, applications, outcomes, and benefits. Seven databases were searched from 1985 to March 2010. Several search terms relating to phr s were used during this process. Two authors independently screened titles and abstracts to determine inclusion status. A second screen of full-text articles, again by two independent members of the research team, ensured that the studies described phr s. All in all, 130 articles met the criteria and their data were extracted manually into a database. The authors concluded that although there is a large amount of survey, observational, cohort/panel, and anecdotal evidence of phr benefits and satisfaction for patients, more research is needed to evaluate the results of phr implementations. Their in-depth analysis of the literature signalled that there is little solid evidence from randomized controlled trials or other studies through the use of phr s. Hence, they suggested that more research is needed that addresses the current lack of understanding of optimal functionality and usability of these systems, and how they can play a beneficial role in supporting patient self-management ( Archer et al., 2011 ).

9.3.4. Forms of Aggregative Reviews

Healthcare providers, practitioners, and policy-makers are nowadays overwhelmed with large volumes of information, including research-based evidence from numerous clinical trials and evaluation studies, assessing the effectiveness of health information technologies and interventions ( Ammenwerth & de Keizer, 2004 ; Deshazo et al., 2009 ). It is unrealistic to expect that all these disparate actors will have the time, skills, and necessary resources to identify the available evidence in the area of their expertise and consider it when making decisions. Systematic reviews that involve the rigorous application of scientific strategies aimed at limiting subjectivity and bias (i.e., systematic and random errors) can respond to this challenge.

Systematic reviews attempt to aggregate, appraise, and synthesize in a single source all empirical evidence that meet a set of previously specified eligibility criteria in order to answer a clearly formulated and often narrow research question on a particular topic of interest to support evidence-based practice ( Liberati et al., 2009 ). They adhere closely to explicit scientific principles ( Liberati et al., 2009 ) and rigorous methodological guidelines (Higgins & Green, 2008) aimed at reducing random and systematic errors that can lead to deviations from the truth in results or inferences. The use of explicit methods allows systematic reviews to aggregate a large body of research evidence, assess whether effects or relationships are in the same direction and of the same general magnitude, explain possible inconsistencies between study results, and determine the strength of the overall evidence for every outcome of interest based on the quality of included studies and the general consistency among them ( Cook, Mulrow, & Haynes, 1997 ). The main procedures of a systematic review involve:

• Formulating a review question and developing a search strategy based on explicit inclusion criteria for the identification of eligible studies (usually described in the context of a detailed review protocol).
• Searching for eligible studies using multiple databases and information sources, including grey literature sources, without any language restrictions.
• Selecting studies, extracting data, and assessing risk of bias in a duplicate manner using two independent reviewers to avoid random or systematic errors in the process.
• Analyzing data using quantitative or qualitative methods.
• Presenting results in summary of findings tables.
• Interpreting results and drawing conclusions.

Many systematic reviews, but not all, use statistical methods to combine the results of independent studies into a single quantitative estimate or summary effect size. Known as meta-analyses , these reviews use specific data extraction and statistical techniques (e.g., network, frequentist, or Bayesian meta-analyses) to calculate from each study by outcome of interest an effect size along with a confidence interval that reflects the degree of uncertainty behind the point estimate of effect ( Borenstein, Hedges, Higgins, & Rothstein, 2009 ; Deeks, Higgins, & Altman, 2008 ). Subsequently, they use fixed or random-effects analysis models to combine the results of the included studies, assess statistical heterogeneity, and calculate a weighted average of the effect estimates from the different studies, taking into account their sample sizes. The summary effect size is a value that reflects the average magnitude of the intervention effect for a particular outcome of interest or, more generally, the strength of a relationship between two variables across all studies included in the systematic review. By statistically combining data from multiple studies, meta-analyses can create more precise and reliable estimates of intervention effects than those derived from individual studies alone, when these are examined independently as discrete sources of information.

The review by Gurol-Urganci, de Jongh, Vodopivec-Jamsek, Atun, and Car (2013) on the effects of mobile phone messaging reminders for attendance at healthcare appointments is an illustrative example of a high-quality systematic review with meta-analysis. Missed appointments are a major cause of inefficiency in healthcare delivery with substantial monetary costs to health systems. These authors sought to assess whether mobile phone-based appointment reminders delivered through Short Message Service ( sms ) or Multimedia Messaging Service ( mms ) are effective in improving rates of patient attendance and reducing overall costs. To this end, they conducted a comprehensive search on multiple databases using highly sensitive search strategies without language or publication-type restrictions to identify all rct s that are eligible for inclusion. In order to minimize the risk of omitting eligible studies not captured by the original search, they supplemented all electronic searches with manual screening of trial registers and references contained in the included studies. Study selection, data extraction, and risk of bias assessments were performed inde­­pen­dently by two coders using standardized methods to ensure consistency and to eliminate potential errors. Findings from eight rct s involving 6,615 participants were pooled into meta-analyses to calculate the magnitude of effects that mobile text message reminders have on the rate of attendance at healthcare appointments compared to no reminders and phone call reminders.

Meta-analyses are regarded as powerful tools for deriving meaningful conclusions. However, there are situations in which it is neither reasonable nor appropriate to pool studies together using meta-analytic methods simply because there is extensive clinical heterogeneity between the included studies or variation in measurement tools, comparisons, or outcomes of interest. In these cases, systematic reviews can use qualitative synthesis methods such as vote counting, content analysis, classification schemes and tabulations, as an alternative approach to narratively synthesize the results of the independent studies included in the review. This form of review is known as qualitative systematic review.

A rigorous example of one such review in the eHealth domain is presented by Mickan, Atherton, Roberts, Heneghan, and Tilson (2014) on the use of handheld computers by healthcare professionals and their impact on access to information and clinical decision-making. In line with the methodological guide­lines for systematic reviews, these authors: (a) developed and registered with prospero ( www.crd.york.ac.uk/ prospero / ) an a priori review protocol; (b) conducted comprehensive searches for eligible studies using multiple databases and other supplementary strategies (e.g., forward searches); and (c) subsequently carried out study selection, data extraction, and risk of bias assessments in a duplicate manner to eliminate potential errors in the review process. Heterogeneity between the included studies in terms of reported outcomes and measures precluded the use of meta-analytic methods. To this end, the authors resorted to using narrative analysis and synthesis to describe the effectiveness of handheld computers on accessing information for clinical knowledge, adherence to safety and clinical quality guidelines, and diagnostic decision-making.

In recent years, the number of systematic reviews in the field of health informatics has increased considerably. Systematic reviews with discordant findings can cause great confusion and make it difficult for decision-makers to interpret the review-level evidence ( Moher, 2013 ). Therefore, there is a growing need for appraisal and synthesis of prior systematic reviews to ensure that decision-making is constantly informed by the best available accumulated evidence. Umbrella reviews , also known as overviews of systematic reviews, are tertiary types of evidence synthesis that aim to accomplish this; that is, they aim to compare and contrast findings from multiple systematic reviews and meta-analyses ( Becker & Oxman, 2008 ). Umbrella reviews generally adhere to the same principles and rigorous methodological guidelines used in systematic reviews. However, the unit of analysis in umbrella reviews is the systematic review rather than the primary study ( Becker & Oxman, 2008 ). Unlike systematic reviews that have a narrow focus of inquiry, umbrella reviews focus on broader research topics for which there are several potential interventions ( Smith, Devane, Begley, & Clarke, 2011 ). A recent umbrella review on the effects of home telemonitoring interventions for patients with heart failure critically appraised, compared, and synthesized evidence from 15 systematic reviews to investigate which types of home telemonitoring technologies and forms of interventions are more effective in reducing mortality and hospital admissions ( Kitsiou, Paré, & Jaana, 2015 ).

9.3.5. Realist Reviews

Realist reviews are theory-driven interpretative reviews developed to inform, enhance, or supplement conventional systematic reviews by making sense of heterogeneous evidence about complex interventions applied in diverse contexts in a way that informs policy decision-making ( Greenhalgh, Wong, Westhorp, & Pawson, 2011 ). They originated from criticisms of positivist systematic reviews which centre on their “simplistic” underlying assumptions ( Oates, 2011 ). As explained above, systematic reviews seek to identify causation. Such logic is appropriate for fields like medicine and education where findings of randomized controlled trials can be aggregated to see whether a new treatment or intervention does improve outcomes. However, many argue that it is not possible to establish such direct causal links between interventions and outcomes in fields such as social policy, management, and information systems where for any intervention there is unlikely to be a regular or consistent outcome ( Oates, 2011 ; Pawson, 2006 ; Rousseau, Manning, & Denyer, 2008 ).

To circumvent these limitations, Pawson, Greenhalgh, Harvey, and Walshe (2005) have proposed a new approach for synthesizing knowledge that seeks to unpack the mechanism of how “complex interventions” work in particular contexts. The basic research question — what works? — which is usually associated with systematic reviews changes to: what is it about this intervention that works, for whom, in what circumstances, in what respects and why? Realist reviews have no particular preference for either quantitative or qualitative evidence. As a theory-building approach, a realist review usually starts by articulating likely underlying mechanisms and then scrutinizes available evidence to find out whether and where these mechanisms are applicable ( Shepperd et al., 2009 ). Primary studies found in the extant literature are viewed as case studies which can test and modify the initial theories ( Rousseau et al., 2008 ).

The main objective pursued in the realist review conducted by Otte-Trojel, de Bont, Rundall, and van de Klundert (2014) was to examine how patient portals contribute to health service delivery and patient outcomes. The specific goals were to investigate how outcomes are produced and, most importantly, how variations in outcomes can be explained. The research team started with an exploratory review of background documents and research studies to identify ways in which patient portals may contribute to health service delivery and patient outcomes. The authors identified six main ways which represent “educated guesses” to be tested against the data in the evaluation studies. These studies were identified through a formal and systematic search in four databases between 2003 and 2013. Two members of the research team selected the articles using a pre-established list of inclusion and exclusion criteria and following a two-step procedure. The authors then extracted data from the selected articles and created several tables, one for each outcome category. They organized information to bring forward those mechanisms where patient portals contribute to outcomes and the variation in outcomes across different contexts.

9.3.6. Critical Reviews

Lastly, critical reviews aim to provide a critical evaluation and interpretive analysis of existing literature on a particular topic of interest to reveal strengths, weaknesses, contradictions, controversies, inconsistencies, and/or other important issues with respect to theories, hypotheses, research methods or results ( Baumeister & Leary, 1997 ; Kirkevold, 1997 ). Unlike other review types, critical reviews attempt to take a reflective account of the research that has been done in a particular area of interest, and assess its credibility by using appraisal instruments or critical interpretive methods. In this way, critical reviews attempt to constructively inform other scholars about the weaknesses of prior research and strengthen knowledge development by giving focus and direction to studies for further improvement ( Kirkevold, 1997 ).

Kitsiou, Paré, and Jaana (2013) provide an example of a critical review that assessed the methodological quality of prior systematic reviews of home telemonitoring studies for chronic patients. The authors conducted a comprehensive search on multiple databases to identify eligible reviews and subsequently used a validated instrument to conduct an in-depth quality appraisal. Results indicate that the majority of systematic reviews in this particular area suffer from important methodological flaws and biases that impair their internal validity and limit their usefulness for clinical and decision-making purposes. To this end, they provide a number of recommendations to strengthen knowledge development towards improving the design and execution of future reviews on home telemonitoring.

9.4. Summary

Table 9.1 outlines the main types of literature reviews that were described in the previous sub-sections and summarizes the main characteristics that distinguish one review type from another. It also includes key references to methodological guidelines and useful sources that can be used by eHealth scholars and researchers for planning and developing reviews.

Typology of Literature Reviews (adapted from Paré et al., 2015).

As shown in Table 9.1 , each review type addresses different kinds of research questions or objectives, which subsequently define and dictate the methods and approaches that need to be used to achieve the overarching goal(s) of the review. For example, in the case of narrative reviews, there is greater flexibility in searching and synthesizing articles ( Green et al., 2006 ). Researchers are often relatively free to use a diversity of approaches to search, identify, and select relevant scientific articles, describe their operational characteristics, present how the individual studies fit together, and formulate conclusions. On the other hand, systematic reviews are characterized by their high level of systematicity, rigour, and use of explicit methods, based on an “a priori” review plan that aims to minimize bias in the analysis and synthesis process (Higgins & Green, 2008). Some reviews are exploratory in nature (e.g., scoping/mapping reviews), whereas others may be conducted to discover patterns (e.g., descriptive reviews) or involve a synthesis approach that may include the critical analysis of prior research ( Paré et al., 2015 ). Hence, in order to select the most appropriate type of review, it is critical to know before embarking on a review project, why the research synthesis is conducted and what type of methods are best aligned with the pursued goals.

9.5. Concluding Remarks

In light of the increased use of evidence-based practice and research generating stronger evidence ( Grady et al., 2011 ; Lyden et al., 2013 ), review articles have become essential tools for summarizing, synthesizing, integrating or critically appraising prior knowledge in the eHealth field. As mentioned earlier, when rigorously conducted review articles represent powerful information sources for eHealth scholars and practitioners looking for state-of-the-art evidence. The typology of literature reviews we used herein will allow eHealth researchers, graduate students and practitioners to gain a better understanding of the similarities and differences between review types.

We must stress that this classification scheme does not privilege any specific type of review as being of higher quality than another ( Paré et al., 2015 ). As explained above, each type of review has its own strengths and limitations. Having said that, we realize that the methodological rigour of any review — be it qualitative, quantitative or mixed — is a critical aspect that should be considered seriously by prospective authors. In the present context, the notion of rigour refers to the reliability and validity of the review process described in section 9.2. For one thing, reliability is related to the reproducibility of the review process and steps, which is facilitated by a comprehensive documentation of the literature search process, extraction, coding and analysis performed in the review. Whether the search is comprehensive or not, whether it involves a methodical approach for data extraction and synthesis or not, it is important that the review documents in an explicit and transparent manner the steps and approach that were used in the process of its development. Next, validity characterizes the degree to which the review process was conducted appropriately. It goes beyond documentation and reflects decisions related to the selection of the sources, the search terms used, the period of time covered, the articles selected in the search, and the application of backward and forward searches ( vom Brocke et al., 2009 ). In short, the rigour of any review article is reflected by the explicitness of its methods (i.e., transparency) and the soundness of the approach used. We refer those interested in the concepts of rigour and quality to the work of Templier and Paré (2015) which offers a detailed set of methodological guidelines for conducting and evaluating various types of review articles.

To conclude, our main objective in this chapter was to demystify the various types of literature reviews that are central to the continuous development of the eHealth field. It is our hope that our descriptive account will serve as a valuable source for those conducting, evaluating or using reviews in this important and growing domain.

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• Cite this Page Paré G, Kitsiou S. Chapter 9 Methods for Literature Reviews. In: Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.
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How do I Write a Literature Review?: #5 Writing the Review

• Step #1: Choosing a Topic
• Step #2: Finding Information
• Step #3: Evaluating Content
• Step #4: Synthesizing Content
• #5 Writing the Review
• Citing Your Sources

WRITING THE REVIEW 

You've done the research and now you're ready to put your findings down on paper. When preparing to write your review, first consider how will you organize your review.

The actual review generally has 5 components:

Abstract  -  An abstract is a summary of your literature review. It is made up of the following parts:

• A contextual sentence about your motivation behind your research topic
• Your thesis statement
• A descriptive statement about the types of literature used in the review
• Summarize your findings
• Conclusion(s) based upon your findings

Introduction :   Like a typical research paper introduction, provide the reader with a quick idea of the topic of the literature review:

• Define or identify the general topic, issue, or area of concern. This provides the reader with context for reviewing the literature.
• Identify related trends in what has already been published about the topic; or conflicts in theory, methodology, evidence, and conclusions; or gaps in research and scholarship; or a single problem or new perspective of immediate interest.
• Establish your reason (point of view) for reviewing the literature; explain the criteria to be used in analyzing and comparing literature and the organization of the review (sequence); and, when necessary, state why certain literature is or is not included (scope)  - 

Body :  The body of a literature review contains your discussion of sources and can be organized in 3 ways-

• Chronological -  by publication or by trend
• Thematic -  organized around a topic or issue, rather than the progression of time
• Methodical -  the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the "methods" of the literature's researcher or writer that you are reviewing

You may also want to include a section on "questions for further research" and discuss what questions the review has sparked about the topic/field or offer suggestions for future studies/examinations that build on your current findings.

Conclusion :  In the conclusion, you should:

Conclude your paper by providing your reader with some perspective on the relationship between your literature review's specific topic and how it's related to it's parent discipline, scientific endeavor, or profession.

Bibliography :   Since a literature review is composed of pieces of research, it is very important that your correctly cite the literature you are reviewing, both in the reviews body as well as in a bibliography/works cited. To learn more about different citation styles, visit the " Citing Your Sources " tab.

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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.

Importance of a Good Literature Review

A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:

• Give a new interpretation of old material or combine new with old interpretations,
• Trace the intellectual progression of the field, including major debates,
• Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
• Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.

Given this, the purpose of a literature review is to:

• Place each work in the context of its contribution to understanding the research problem being studied.
• Describe the relationship of each work to the others under consideration.
• Identify new ways to interpret prior research.
• Reveal any gaps that exist in the literature.
• Resolve conflicts amongst seemingly contradictory previous studies.
• Identify areas of prior scholarship to prevent duplication of effort.
• Point the way in fulfilling a need for additional research.
• Locate your own research within the context of existing literature [very important].

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.

Types of Literature Reviews

It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.

Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.

Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.

Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

NOTE : Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.

Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews."  Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

Structure and Writing Style

I.  Thinking About Your Literature Review

The structure of a literature review should include the following in support of understanding the research problem :

• An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
• Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
• An explanation of how each work is similar to and how it varies from the others,
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.

The critical evaluation of each work should consider :

• Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
• Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
• Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Persuasiveness -- which of the author's theses are most convincing or least convincing?
• Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

II.  Development of the Literature Review

Four Basic Stages of Writing 1.  Problem formulation -- which topic or field is being examined and what are its component issues? 2.  Literature search -- finding materials relevant to the subject being explored. 3.  Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4.  Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.

Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1.  Roughly how many sources would be appropriate to include? 2.  What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3.  Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4.  Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5.  Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.

III.  Ways to Organize Your Literature Review

Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.

Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:

• Current Situation : Information necessary to understand the current topic or focus of the literature review.
• Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
• History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
• Standards : Description of the way in which you present your information.
• Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?

IV.  Writing Your Literature Review

Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.

Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.

V.  Common Mistakes to Avoid

These are the most common mistakes made in reviewing social science research literature.

• Sources in your literature review do not clearly relate to the research problem;
• You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
• Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
• Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
• Does not describe the search procedures that were used in identifying the literature to review;
• Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
• Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.

Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.

Writing Tip

Break Out of Your Disciplinary Box!

Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.

Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.

Another Writing Tip

Don't Just Review for Content!

While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:

• How are they organizing their ideas?
• What methods have they used to study the problem?
• What theories have been used to explain, predict, or understand their research problem?
• What sources have they cited to support their conclusions?
• How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?

When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.

Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.

Yet Another Writing Tip

When Do I Know I Can Stop Looking and Move On?

Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:

• Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research?  Does it forge a new path? Or, does is merely add more of the same thing being said?
• Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
• Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.

Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

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Literature Reviews

• What is a literature review?
• Steps in the Literature Review Process
• Define your research question
• Determine inclusion and exclusion criteria
• Choose databases and search
• Review Results
• Synthesize Results
• Analyze Results
• Librarian Support

What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

Meryl Brodsky : Communication and Information Studies

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Susan Macicak : Linguistics

Imelda Vetter : Dell Medical School

For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

• October 26, 2022 recording
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How to write a literature review introduction (+ examples)

The introduction to a literature review serves as your reader’s guide through your academic work and thought process. Explore the significance of literature review introductions in review papers, academic papers, essays, theses, and dissertations. We delve into the purpose and necessity of these introductions, explore the essential components of literature review introductions, and provide step-by-step guidance on how to craft your own, along with examples.

Why you need an introduction for a literature review

When you need an introduction for a literature review, what to include in a literature review introduction, examples of literature review introductions, steps to write your own literature review introduction.

A literature review is a comprehensive examination of the international academic literature concerning a particular topic. It involves summarizing published works, theories, and concepts while also highlighting gaps and offering critical reflections.

In academic writing , the introduction for a literature review is an indispensable component. Effective academic writing requires proper paragraph structuring to guide your reader through your argumentation. This includes providing an introduction to your literature review.

It is imperative to remember that you should never start sharing your findings abruptly. Even if there isn’t a dedicated introduction section .

Instead, you should always offer some form of introduction to orient the reader and clarify what they can expect.

There are three main scenarios in which you need an introduction for a literature review:

• Academic literature review papers: When your literature review constitutes the entirety of an academic review paper, a more substantial introduction is necessary. This introduction should resemble the standard introduction found in regular academic papers.
• Literature review section in an academic paper or essay: While this section tends to be brief, it’s important to precede the detailed literature review with a few introductory sentences. This helps orient the reader before delving into the literature itself.
• Literature review chapter or section in your thesis/dissertation: Every thesis and dissertation includes a literature review component, which also requires a concise introduction to set the stage for the subsequent review.

You may also like: How to write a fantastic thesis introduction (+15 examples)

It is crucial to customize the content and depth of your literature review introduction according to the specific format of your academic work.

In practical terms, this implies, for instance, that the introduction in an academic literature review paper, especially one derived from a systematic literature review , is quite comprehensive. Particularly compared to the rather brief one or two introductory sentences that are often found at the beginning of a literature review section in a standard academic paper. The introduction to the literature review chapter in a thesis or dissertation again adheres to different standards.

Here’s a structured breakdown based on length and the necessary information:

Academic literature review paper

The introduction of an academic literature review paper, which does not rely on empirical data, often necessitates a more extensive introduction than the brief literature review introductions typically found in empirical papers. It should encompass:

• The research problem: Clearly articulate the problem or question that your literature review aims to address.
• The research gap: Highlight the existing gaps, limitations, or unresolved aspects within the current body of literature related to the research problem.
• The research relevance: Explain why the chosen research problem and its subsequent investigation through a literature review are significant and relevant in your academic field.
• The literature review method: If applicable, describe the methodology employed in your literature review, especially if it is a systematic review or follows a specific research framework.
• The main findings or insights of the literature review: Summarize the key discoveries, insights, or trends that have emerged from your comprehensive review of the literature.
• The main argument of the literature review: Conclude the introduction by outlining the primary argument or statement that your literature review will substantiate, linking it to the research problem and relevance you’ve established.
• Preview of the literature review’s structure: Offer a glimpse into the organization of the literature review paper, acting as a guide for the reader. This overview outlines the subsequent sections of the paper and provides an understanding of what to anticipate.

By addressing these elements, your introduction will provide a clear and structured overview of what readers can expect in your literature review paper.

Regular literature review section in an academic article or essay

Most academic articles or essays incorporate regular literature review sections, often placed after the introduction. These sections serve to establish a scholarly basis for the research or discussion within the paper.

In a standard 8000-word journal article, the literature review section typically spans between 750 and 1250 words. The first few sentences or the first paragraph within this section often serve as an introduction. It should encompass:

• An introduction to the topic: When delving into the academic literature on a specific topic, it’s important to provide a smooth transition that aids the reader in comprehending why certain aspects will be discussed within your literature review.
• The core argument: While literature review sections primarily synthesize the work of other scholars, they should consistently connect to your central argument. This central argument serves as the crux of your message or the key takeaway you want your readers to retain. By positioning it at the outset of the literature review section and systematically substantiating it with evidence, you not only enhance reader comprehension but also elevate overall readability. This primary argument can typically be distilled into 1-2 succinct sentences.

In some cases, you might include:

• Methodology: Details about the methodology used, but only if your literature review employed a specialized method. If your approach involved a broader overview without a systematic methodology, you can omit this section, thereby conserving word count.

By addressing these elements, your introduction will effectively integrate your literature review into the broader context of your academic paper or essay. This will, in turn, assist your reader in seamlessly following your overarching line of argumentation.

Introduction to a literature review chapter in thesis or dissertation

The literature review typically constitutes a distinct chapter within a thesis or dissertation. Often, it is Chapter 2 of a thesis or dissertation.

Some students choose to incorporate a brief introductory section at the beginning of each chapter, including the literature review chapter. Alternatively, others opt to seamlessly integrate the introduction into the initial sentences of the literature review itself. Both approaches are acceptable, provided that you incorporate the following elements:

• Purpose of the literature review and its relevance to the thesis/dissertation research: Explain the broader objectives of the literature review within the context of your research and how it contributes to your thesis or dissertation. Essentially, you’re telling the reader why this literature review is important and how it fits into the larger scope of your academic work.
• Primary argument: Succinctly communicate what you aim to prove, explain, or explore through the review of existing literature. This statement helps guide the reader’s understanding of the review’s purpose and what to expect from it.
• Preview of the literature review’s content: Provide a brief overview of the topics or themes that your literature review will cover. It’s like a roadmap for the reader, outlining the main areas of focus within the review. This preview can help the reader anticipate the structure and organization of your literature review.
• Methodology: If your literature review involved a specific research method, such as a systematic review or meta-analysis, you should briefly describe that methodology. However, this is not always necessary, especially if your literature review is more of a narrative synthesis without a distinct research method.

By addressing these elements, your introduction will empower your literature review to play a pivotal role in your thesis or dissertation research. It will accomplish this by integrating your research into the broader academic literature and providing a solid theoretical foundation for your work.

Comprehending the art of crafting your own literature review introduction becomes significantly more accessible when you have concrete examples to examine. Here, you will find several examples that meet, or in most cases, adhere to the criteria described earlier.

Example 1: An effective introduction for an academic literature review paper

To begin, let’s delve into the introduction of an academic literature review paper. We will examine the paper “How does culture influence innovation? A systematic literature review”, which was published in 2018 in the journal Management Decision.

The entire introduction spans 611 words and is divided into five paragraphs. In this introduction, the authors accomplish the following:

• In the first paragraph, the authors introduce the broader topic of the literature review, which focuses on innovation and its significance in the context of economic competition. They underscore the importance of this topic, highlighting its relevance for both researchers and policymakers.
• In the second paragraph, the authors narrow down their focus to emphasize the specific role of culture in relation to innovation.
• In the third paragraph, the authors identify research gaps, noting that existing studies are often fragmented and disconnected. They then emphasize the value of conducting a systematic literature review to enhance our understanding of the topic.
• In the fourth paragraph, the authors introduce their specific objectives and explain how their insights can benefit other researchers and business practitioners.
• In the fifth and final paragraph, the authors provide an overview of the paper’s organization and structure.

In summary, this introduction stands as a solid example. While the authors deviate from previewing their key findings (which is a common practice at least in the social sciences), they do effectively cover all the other previously mentioned points.

Example 2: An effective introduction to a literature review section in an academic paper

The second example represents a typical academic paper, encompassing not only a literature review section but also empirical data, a case study, and other elements. We will closely examine the introduction to the literature review section in the paper “The environmentalism of the subalterns: a case study of environmental activism in Eastern Kurdistan/Rojhelat”, which was published in 2021 in the journal Local Environment.

The paper begins with a general introduction and then proceeds to the literature review, designated by the authors as their conceptual framework. Of particular interest is the first paragraph of this conceptual framework, comprising 142 words across five sentences:

“ A peripheral and marginalised nationality within a multinational though-Persian dominated Iranian society, the Kurdish people of Iranian Kurdistan (a region referred by the Kurds as Rojhelat/Eastern Kurdi-stan) have since the early twentieth century been subject to multifaceted and systematic discriminatory and exclusionary state policy in Iran. This condition has left a population of 12–15 million Kurds in Iran suffering from structural inequalities, disenfranchisement and deprivation. Mismanagement of Kurdistan’s natural resources and the degradation of its natural environmental are among examples of this disenfranchisement. As asserted by Julian Agyeman (2005), structural inequalities that sustain the domination of political and economic elites often simultaneously result in environmental degradation, injustice and discrimination against subaltern communities. This study argues that the environmental struggle in Eastern Kurdistan can be asserted as a (sub)element of the Kurdish liberation movement in Iran. Conceptually this research is inspired by and has been conducted through the lens of ‘subalternity’ ” ( Hassaniyan, 2021, p. 931 ).

In this first paragraph, the author is doing the following:

• The author contextualises the research
• The author links the research focus to the international literature on structural inequalities
• The author clearly presents the argument of the research
• The author clarifies how the research is inspired by and uses the concept of ‘subalternity’.

Thus, the author successfully introduces the literature review, from which point onward it dives into the main concept (‘subalternity’) of the research, and reviews the literature on socio-economic justice and environmental degradation.

While introductions to a literature review section aren’t always required to offer the same level of study context detail as demonstrated here, this introduction serves as a commendable model for orienting the reader within the literature review. It effectively underscores the literature review’s significance within the context of the study being conducted.

Examples 3-5: Effective introductions to literature review chapters

The introduction to a literature review chapter can vary in length, depending largely on the overall length of the literature review chapter itself. For example, a master’s thesis typically features a more concise literature review, thus necessitating a shorter introduction. In contrast, a Ph.D. thesis, with its more extensive literature review, often includes a more detailed introduction.

Numerous universities offer online repositories where you can access theses and dissertations from previous years, serving as valuable sources of reference. Many of these repositories, however, may require you to log in through your university account. Nevertheless, a few open-access repositories are accessible to anyone, such as the one by the University of Manchester . It’s important to note though that copyright restrictions apply to these resources, just as they would with published papers.

Master’s thesis literature review introduction

The first example is “Benchmarking Asymmetrical Heating Models of Spider Pulsar Companions” by P. Sun, a master’s thesis completed at the University of Manchester on January 9, 2024. The author, P. Sun, introduces the literature review chapter very briefly but effectively:

PhD thesis literature review chapter introduction

The second example is Deep Learning on Semi-Structured Data and its Applications to Video-Game AI, Woof, W. (Author). 31 Dec 2020, a PhD thesis completed at the University of Manchester . In Chapter 2, the author offers a comprehensive introduction to the topic in four paragraphs, with the final paragraph serving as an overview of the chapter’s structure:

PhD thesis literature review introduction

The last example is the doctoral thesis Metacognitive strategies and beliefs: Child correlates and early experiences Chan, K. Y. M. (Author). 31 Dec 2020 . The author clearly conducted a systematic literature review, commencing the review section with a discussion of the methodology and approach employed in locating and analyzing the selected records.

Having absorbed all of this information, let’s recap the essential steps and offer a succinct guide on how to proceed with creating your literature review introduction:

• Contextualize your review : Begin by clearly identifying the academic context in which your literature review resides and determining the necessary information to include.
• Outline your structure : Develop a structured outline for your literature review, highlighting the essential information you plan to incorporate in your introduction.
• Literature review process : Conduct a rigorous literature review, reviewing and analyzing relevant sources.
• Summarize and abstract : After completing the review, synthesize the findings and abstract key insights, trends, and knowledge gaps from the literature.
• Craft the introduction : Write your literature review introduction with meticulous attention to the seamless integration of your review into the larger context of your work. Ensure that your introduction effectively elucidates your rationale for the chosen review topics and the underlying reasons guiding your selection.

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Mechanical stimulation devices for mechanobiology studies: a market, literature, and patents review

• Open access
• Published: 01 April 2023
• Volume 6 , pages 340–371, ( 2023 )

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• F. Melo-Fonseca   ORCID: orcid.org/0000-0001-8881-5324 1 , 2 , 3 ,
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Significant advancements in various research and technological fields have contributed to remarkable findings on the physiological dynamics of the human body. To more closely mimic the complex physiological environment, research has moved from two-dimensional (2D) culture systems to more sophisticated three-dimensional (3D) dynamic cultures. Unlike bioreactors or microfluidic-based culture models, cells are typically seeded on polymeric substrates or incorporated into 3D constructs which are mechanically stimulated to investigate cell response to mechanical stresses, such as tensile or compressive. This review focuses on the working principles of mechanical stimulation devices currently available on the market or custom-built by research groups or protected by patents and highlights the main features still open to improvement. These are the features which could be focused on to perform, in the future, more reliable and accurate mechanobiology studies.

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Contextualization

The adult human body is composed of approximately 37 trillion cells, all synchronized to maintain equilibrium [ 1 ]. Cells reside in a complex and dynamic microenvironment containing biological, chemical, physical, and mechanical cues which often regulate cell proliferation, migration, differentiation, and function, and ultimately, may be responsible for the development of disease [ 2 ]. To study and understand how cells respond to mechanical stimuli or how host cells will behave upon the implantation of biomaterials, researchers use mechanical stimulation devices. These devices subject biomaterials to a particular mechanical stress with the aim of stimulating cells through deformation of the biomaterials. Devices which are currently commercially available offer limited customization and restricted force measurement capabilities [ 3 , 4 ]. As a consequence, a wide variety of apparatuses, with varying levels of sophistication, design, functionality, and precision, have been custom-built by research groups to meet particular needs, while others are protected by patents. This review focuses on the working principles, functionality, and main operational features of a number of mechanical stimulation devices developed over the past years, and highlights the main features still open to improvement.

The cellular microenvironment

All cells are in permanent interaction with the surrounding microenvironment, including the extracellular matrix (ECM) and neighbouring cells. That interaction is based on a combination of multiple cues, including biological and physical cues able to influence cell behaviour [ 5 , 6 ]. Cells are constantly and cyclically subjected to external forces whose type and magnitude are highly variable and dependent on location [ 7 ]. These forces are crucial from the beginning of cell life: throughout the development of embryos, and in everyday activities, in which cells experience shear stress during breathing and blood flow, or tensile and compressive stresses from skeletal muscle contraction, joint loading, and tendon/ligament stretching [ 8 , 9 , 10 , 11 ]. Their ability to sense externally imposed forces and mechanical properties of the surrounding ECM is denominated “cell mechanosensing” [ 12 ]. These signals are later converted into changes in intracellular biochemistry and gene expression, a process often referred to as “mechanotransduction” [ 13 ]. Mechanical stimuli include not only externally imposed forces (namely tensile, compressive, and shear forces), but also intrinsic cellular tensions generated by active cell contraction [ 7 ]. In fact, besides the intracellular response to dynamic modifications of the ECM, cells are also able to influence the environment, leading to a reciprocal interaction [ 7 , 11 ]. Both outside-in and inside-out pathways exist in mechanotransduction processes, and are able to trigger signalling cascades [ 14 , 15 ]. In this sense, the environment plays an important role in many cellular processes, such as cellular adhesion, migration, proliferation, differentiation, and apoptosis [ 15 ]. Given the importance of mechanical interactions in cellular behaviour, mechanobiology has emerged as a novel interdisciplinary field combining biology, mechanics, and engineering, which aims to understand how cells sense and behave in response to mechanical stimuli [ 7 , 11 , 16 , 17 ]. Over the past few decades, researchers have developed systems to control the cellular microenvironment and, while some focus on improving cell culture conditions, others aim to study the effects of a particular mechanical stimulus on cells by using unique cells or biomaterial-based constructs.

Moving from 2D to 3D models

Biological systems are organized into several levels of structural organization, becoming more complex as the length scale increases. Beginning at the micrometre scale, cells assemble to form tissues, which are organized into organs, which together form the organism, the highest level of organization, on the metre scale. Biological model systems range from simplified two-dimensional (2D) cell cultures to more complex three-dimensional (3D) cell cultures, organoids, tissue explants, and model organisms, such as the mouse [ 2 ]. As the complexity rises, the associated cost and physiological relevance increase, while experimental accessibility decreases [ 2 ].

The 2D and 3D cell culture systems discussed below are illustrated in Fig.  1 , in both static and dynamic modes. In conventional and static cell cultures, the nutrient supply is maintained by frequently changing the culture medium. Primary cells or established cell lines may be cultured as a 2D monolayer, in the case of an adherent culture, or as a cell suspension known as a “suspension culture”. Although monolayer cultures are easily manipulated, used worldwide in life-science research, and still accepted as the gold standard, cells are highly anisotropic. This is why it has been experimentally observed that even within a particular cell line, cellular responses may differ for an identical mechanical input [ 18 ]. Moreover, it has been reported that cells may lose some differentiated characteristics [ 19 ] and that conventional 2D culture models, whether in Petri dishes or culture flasks, do not replicate the dynamic in vivo 3D microenvironment [ 2 ]. As a consequence, over the past decades, researchers have focused on more complex cell culture models which include cell seeding on prefabricated scaffolds or incorporate cells into 3D scaffolds (usually hydrogels made of synthetic polymers). These materials allow cellular spatial organization into functional cell-based constructs. In order to keep up with continuously more complex and demanding research, bioreactor systems were developed for numerous applications, for example, in the context of cell biology research and regenerative medicine therapies. While the absence of media mixing or circulation in a static aqueous environment leads to limited diffusion of fluids or gases and contributes to cell-waste accumulation and nutrition depletion [ 5 , 20 ], 3D models with continuously mixed media in a dynamic culture allow homogeneous media and cell dispersion, better reproducing the in vivo spatial and biomechanical complexity [ 19 ]. Three-dimensional culture systems, particularly bioreactors, are not the scope of this review, but extensive works on this topic may be easily found in the literature [ 2 , 20 , 21 , 22 , 23 ]. Briefly, fluid-flow-induced bioreactors are designed to enhance nutrient supply to cell cultures and replicate tissue-specific conditions [ 24 ]. They are often grouped into fed-batch [ 25 ], spinner-flask [ 26 ], rotating [ 24 , 27 ], and perfusion bioreactors [ 21 , 28 ]. Despite the continuous media agitation in bioreactors, an efficient supply of gases and nutrients is not always assured and sample handling and maintenance of sterility are challenging. Because of the constraints related to bioreactor size, cost, and time consumption when running parallel multiple experiments, the reactor volumes in microfluidic systems can be reduced down to picolitres, while assuring a laminal-flow pattern [ 29 , 30 ]. In addition to the decrease in reagent consumption, the culture environment is particularly controlled, because cell shape, dimensionality, and density are tightly regulated in 10–100 μm channels [ 31 , 32 ]. In the category of micro-engineered devices, lab-on-a-chip-based devices are commonly used for point-of-care diagnostics and are characterized by easy handling and high performance of body fluid analyses [ 33 ]. Organ-on-a-chip devices can be used for culturing cells, spheroids, organoids, and tissue biopsies and, among their final applications, can be used for drug screening and development, disease modelling, and the study of human physiology, due to their capability of closely replicating the dynamic microenvironment of living organs [ 30 , 34 ]. However, the resultant fluid-flow-induced shear stresses may induce cell damage, and current devices lack automation and well-defined protocols [ 34 ]. In contrast to bioreactors, microfluidic-based culture models (or bioreactors on a chip) offer optimized culture conditions and precise control over the chemical and physical cellular environment through the integration of sensors [ 29 ].

Cell culture models may be in a static or dynamic mode. In 2D monolayer cultures, adherent cells are in contact with the culture vessel, neighbouring cells, and the culture medium. In non-adherent plates, 3D spheroids are grown in suspension, either without or with medium agitation (fed-batch bioreactor). In spinner-flask bioreactors, cell dispersion or cell-based constructs attached to a needle are in contact with a homogeneous medium due to agitation and medium perfusion. Rotating wall vessels enable cell culture mixing without an internal stirring mechanism by definition of a proper rotation speed. Perfusion bioreactors use continuous and fresh medium perfusion through cell-based constructs, provided by peristaltic pumps. Microfluidic systems are used for culturing and monitoring of both adherent and non-adherent cells. The fluid dynamics is represented by the red arrow

Two-dimensional culture models are based on a cell monolayer in which cells are forced to adapt to an artificial, flat, and rigid surface [ 27 ], and thus do not provide meaningful information regarding the real dynamics that living cells and tissues experience. Therefore, 3D culture models have greatly increased in number and sophistication, and have the capability of more closely replicating the dynamic microenvironment. They are also more experimentally tractable than model organisms. Despite the fact that bioreactors and microfluidic-based platforms are attractive devices for transporting nutrients and thus improving overall cell culture conditions [ 2 , 35 ], fluid-flow-induced shear stresses cannot be measured in this setting; thus, although this shear stress is considered an important contribution to cell metabolism, it cannot be considered as a mechanical input for mechanotransduction studies.

In the context of mechanobiology, external force can be applied through direct methods such as micropipette aspiration [ 36 , 37 , 38 ], atomic-force microscopy [ 38 , 39 , 40 , 41 ], and substrate deformation [ 32 , 42 , 43 , 44 ]. Indirect methods can also be used, in which cells are, for example, subjected to optical or magnetic fields [ 45 , 46 , 47 ]. In direct methods, a generated and controlled force is applied directly on cells, leading, in some cases, to a large global cell strain. On the other hand, indirect methods allow researchers to monitor deformation in different regions of a cell, but not to precisely control or measure the applied stress [ 32 , 47 ].

Mechanical stimulation devices have been developed to study cellular response to an externally applied mechanical stimulus or to mimic physiological dynamics to perform more reliable studies. For example, one can apply compressive or tensile forces on cells in a controlled way via biomaterials, as illustrated in Fig.  2 . Typically, these devices consist of a culture medium vessel, a specific space for the cell-based construct/substrate, and clamping parts to apply tensile or compressive loading in a controlled computed way [ 21 ]. Furthermore, some devices allow real-time monitoring by the use of chambers composed of light-transparent materials and multi-chamber configurations for parallel experiments [ 21 ]. Individual components, such as biomaterials, ECM, and soluble and mechanical cues, may be integrated in these systems to closely mimic the in vivo environment and study physiology and screen therapeutics.

Examples of mechanical stimulation devices used for mechanobiology studies. The commonly studied mechanical stresses are compressive and tensile stresses, either applied to cells incorporated inside 3D constructs (left) or cells seeded on a flexible substrate (right). The movement imposed on the biomaterials is represented by the red arrow

Emerging mechanical stimulation devices

Mechanical stimulation devices have gained interest due to their potential for replicating mechanical cues observed in the in vivo microenvironment, controlling mechanical and physical properties with precision, and in some cases, allowing simultaneous analysis [ 48 , 49 ]. Mechanical strains in a given material obtained by applying either tensile or compressive stresses in any direction and at controlled loading features, such as strain magnitude and frequency, create a mechanical strain environment around the cultured cells. The strain profile obtained by such substrate deformation may occur in one of the three different modes illustrated in Fig.  3 .

The substrate on which cells (represented by green circles) are cultured may be subjected to different strain modes: uniaxial, biaxial, or equiaxial, as a consequence of substrate movement imposed by the load

Novel and more complex devices have been developed to assure optimal cellular conditions during manipulation (e.g., application of a particular mechanical stimulus) and analyse the corresponding cellular behaviour in small-scale volumes. Some of the operational features of these mechanical stimulation devices are summarized in Table 1 .

Depending on the goal of a particular study and consequently of the experimental design, cells may be seeded directly on the substrate or incorporated in functional constructs. Scaffolds or cell-based constructs are 3D structures often used to regulate the environment of cells, and in this sense, cells can be manipulated by controlling the mechanical properties of the scaffold, such as elasticity, rigidity, and strain. Natural scaffolds are made of naturally derived materials, namely collagen, fibrin, and components of decellularized tissues, whereas fully synthetic matrices are often composed of poly(dimethylsiloxane) (PDMS) and poly(L-lactide-co-glycolide) (PLGA) [ 27 ]. One of the most common materials used in mechanobiology research is PDMS, because it is non-cytotoxic, autoclavable, and flexible. Furthermore, it has high optical transparency and low auto-fluorescence, which allows cell analysis by fluorescence and optical imaging techniques [ 7 , 50 ]. Hydrogels are biocompatible and biomimetic 3D structures which, once again, facilitate imaging because the cellular behaviour in their interior can be monitored. Moreover, hydrogels are typically used to apply mechanical stimuli on cells because they allow a uniform distribution of stresses throughout the structure [ 21 ].

One of the most important concerns in mechanobiology studies is to ensure aseptic conditions during experiments. Therefore, all parts of the mechanical stimulation device are assembled inside a laminal-flow biosafety cabinet and then the complete and mounted device along with its electronic components is placed in a typical culture incubator, allowing maximally sterile conditions and, when required, a long-term experiment. As already mentioned, confocal imaging is often preferable to upright microscopy techniques, mainly to overcome issues related to device size constraints. Therefore, the design of some devices considers the overall device dimensions to ensure that it fits in the microscope chamber, and the incorporation of a glass coverslip or other materials with similar optical properties to allow high-magnification imaging of the cultured or encapsulated cells, for example, for performing live imaging studies [ 32 , 42 , 51 , 52 ]. Other developments are intended to produce high-throughput capabilities, such as by increasing the number of wells/chambers which can be loaded simultaneously [ 51 , 53 , 54 , 55 , 56 , 57 ].

Commercially available cell-stimulation devices

In vitro mechanical stimulation devices have been developed to apply specific mechanical stimuli to biomaterials and, in this way, stimulate cells, for example, as they would be stimulated by external cues typically observed in physiological conditions. Some tension and compression devices are available on the market, and the most well-known companies are FLEXCELL International Corporation, TA Instruments, CellScale, IonOptix, BISS, and Strex. Some features of their commercially available products, including the type of mechanical stimulus and the maximum strain and frequency that can be applied, are summarized in Table 2 . Figure  4 is a graphical representation of the maximum strain/displacement and frequency provided by the device models.

Graphical arrangement of the commercially available mechanical stimulation devices according to their maximum strain/displacement and frequency

Some of the commercialized devices may be used to evaluate a variety of specimens, including cells seeded in monolayers, 3D cell-seeded constructs (e.g. hydrogels), natural tissues, or bioartificial tissue samples. Stretching devices commercialized by FLEXCELL use regulated vacuum pressure and positive air pressure to deform flexible-bottomed culture plates. Depending on the type of culture plate, equibiaxial or uniaxial tension may be applied. Flexcell FX-2000 and FX-4000 created by FLEXCELL International Corporation, and recently upgraded to FX-6000 T, were used to promote tensile loading [ 58 , 59 , 60 , 61 ].

The Flexcell FX-2000 cell-strain unit is composed of a circular silicone rubber membrane at the bottom of each well of the culture plate, in which biaxial strain is regulated by applying vacuum, promoting a multi-radial uniform stretch. One group exposed flexor tendon cells to biaxial tensile strain of 0.0075% at 1 Hz and analysed the formation and organization of the actin stress-fibre network and cell–cell adherent junctions under loading [ 58 ]. In another study, the same Flexcell unit was used to apply an equibiaxial cyclic strain of 3% at 0.25 Hz (2 s on, 2 s off) to human mesenchymal stem cells (hMSCs) for 16 days, which decreased proliferation and stimulated matrix mineralization over unstrained cells (Figs. 5 a– 5 c) [ 59 ]. Human embryonic stem cells (hESCs) were cultured on BioFlex culture plates coated with Matrigel and exposed to a biaxial 10% membrane strain for 10 cycles/min using the FX-4000 device [ 61 ]. The mechanical strain inhibited hESC differentiation, but self-renewal was promoted compared to an unstrained control [ 61 ]. Porcine valve interstitial cells and bone-marrow-derived hMSCs (bm-hMSCs) were cultured on BioFlex culture plates and exposed to a biaxial (radial and circumferential) tensile strain of 7%, 10%, 14%, and 20% respectively at 0.6 Hz for 4 days [ 62 ]. The strain magnitudes, which were homogenously distributed throughout the membrane, had an impact on collagen production [ 62 ]. More recently, the FX-6000 T Tension System was used on vascular smooth muscle cells derived from human-induced pluripotent stem cells (hiPSCs-VSMCs) [ 63 ]. Uniaxial cyclic tensile strain of 2.5% at 2.75 Hz applied for a period of 48 h enhanced the expression of VSMC and ECM markers and also the formation of phalloidin, mostly in a perpendicular direction to the tensile loading direction [ 63 ]. A Flexcell FX-4000 strain unit was used by Sumanasinghe et al. to apply an uniaxial cyclic tensile strain to bm-hMSCs seeded on linear 3D type I collagen matrices [ 60 ]. Cyclic tensile strains of 10% and 12% at 1 Hz induced osteogenic differentiation compared to unstrained controls after 1 and 2 weeks, without osteogenic supplements [ 60 ].

Cellular results of studies which made use of commercially available devices. Von Kossa staining of cell layers after 16 days in culture showed that compared to the unstrained condition ( a ), hMSCs that underwent mechanical strain imposed by Flexcell FX-2000 had greater matrix mineralization ( b ), as corroborated by measurement of matrix-deposited calcium ( c ) (reproduced from [ 59 ], Copyright 2003, with permission from Elsevier). d Sarcomere length analysis by actin (ACTN, red) and nuclei (DAPI, cyan) staining of samples: non-conditioned (NC), electrically conditioned (E), mechanically conditioned by an IonOptix C-stretch (M), and electromechanically conditioned (EM) (scale bar: 25 mm). Results for different conditioning procedures (1 Hz 3 d, 2 Hz 3 d, and 1 Hz 7 d) are shown in a boxplot ( e ) (reproduced from [ 64 ], Copyright 2017, with permission from Elsevier). Empty and non-loaded scaffolds were loaded by a TA Instruments BioDynamic device coupled with an Electroforce testing machine, then cut into cross sections and stained with Sirius red (for collagen) ( f ) and alizarin red (for calcium) ( g ). Absorbance of MTS (for cell-viability assessment), alizarin red, and Sirius red per loaded scaffold at day 20 was normalized to a paired non-loaded scaffold (mean±SD) ( h ), and showed an increase of matrix mineralization after loading (reproduced from [ 66 ], Copyright 2009, with permission from Elsevier). i Expression of gremlin-1 (Grem1) protein (green) in mouse primary chondrocytes increased 24 h after tensile stress loading (stress+) was applied with the Strex STB-140 system, compared to the unloading condition (stress−) (scale bar: 50 μm). j An acceleration of mouse osteoarthritis development after surgical induction was observed through safranin O staining and gremlin-1 immunofluorescence. Scale bars: 100 μm and 50 μm, respectively (reproduced from [ 69 ] authored by Chang et al. under the Creative Commons license CC BY 4.0). hMSCs: human mesenchymal stem cells

Commercialized by IonOptix, C-Pace EM is a multi-mode electromechanical stimulator which can be coupled to the C-Stretch system. This stimulator was used to apply electrical, mechanical, and combined electromechanical stimulation to human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) cultured on fibronectin-coated PDMS [ 64 ]. A uniaxial cyclic tensile strain of 5% was applied at 1 Hz for 3 or 7 days and, with regard to electromechanical stimulation, cells were also stimulated with an electrical field of 3 V/cm and 4 ms biphasic pulse duration at the end of the mechanical stimulus hold phase to mimic the isovolumetric contraction. All three stimulus modes resulted in stress-fibre formation and sarcomeric length shortening, but upon electromechanical stimulus the transmembrane calcium current significantly decreased (Figs. 5 d and 5 e) [ 64 ].

A BioDynamic™ chamber mounted on an ELF3200 mechanical testing machine from the TA Instruments group was used in compressive loading studies [ 65 , 66 ]. Five per cent global strain was applied by cyclic compressive loading (for 2 h on day 9 and then every 5 days up to and including day 19) to hMSCs cultured in 3D polyurethane (PU) scaffolds, and was found to promote osteogenic differentiation and mineralized matrix production [ 65 ]. MLO-A5 osteoblastic cells cultured on PU open-cell foam scaffolds were exposed to a compressive strain of 5% at 1 Hz (for 2 h per day on days 5, 10, and 15 of culture), which promoted the production of mineralized matrix (Figs. 5 f– 5 h) [ 66 ]. Endothelial progenitor cells (EPCs) isolated from rat bone-marrow were seeded in demineralized bone matrix (DBM) scaffolds under cyclic compressive loading. Cell-based constructs were placed in a BioDynamic ELF5110 device, and after being subjected to 5% strain at 1 Hz for 4 h/day for 7 days, proliferation of EPCs increased [ 67 ].

Cell tensile loading systems from Strex are reported in the literature for diverse purposes, including the evaluation of cell adhesion and mechanotransduction studies. Meniscal root and horn cells were cultured on rat tail COL1-coated polydimethylsiloxane and subjected to 2 h and 4 h treatment with 5% and 10% uniaxial cyclic tensile strain at 0.5 Hz, using a STB-140 system. The density of both root and horn cells was reduced after mechanical treatment, whereas expression of the chondrocyte-associated genes SOX9 and COL2A1 was significantly enhanced [ 68 ]. Using the same loading system, mouse primary chondrocytes were seeded into silicon stretch chambers coated with fibronectin, and after 48 h were subjected to cyclic tensile loading (0.5 Hz, 10% elongation) for 30 min in a CO 2 incubator. The excessive loading accelerated osteoarthritis development by inducing gremlin-1 (Figs. 5 i and 5 j) [ 69 ]. In a different study, Murali et al. seeded hMSCs onto silicone chambers coated with COL1 and subjected them to tensile loading at 1 Hz frequency and 8% strain for 6, 24, 48, and 72 h, using the ST-140 model. They suggested that when subjected to uniaxial loading, hMSCs underwent tenogenic differentiation through activation of epithelial sodium channels [ 70 ]. Takahashi et al. seeded normal human lung fibroblasts onto silicon chambers coated with COL1, and a uniaxial sinusoidal cyclic tensile loading of 30 cycles/min was applied for 10 min using the ST-140 model. The concentrations of ATP in the supernatant were significantly elevated by 20% strain, but not by 4% strain. The researchers also visualized ATP release during cell stretch in real time, using the NS-600 W model. Following a single uniaxial tensile strain of 22% for 1 s duration, the release of ATP continued and increased in intensity [ 71 ].

Besides application of tensile or compressive stresses, all models of TA Instruments presented in Table 2 include pulsatile stimulation. For example, the BioDynamic 5170 and BioDynamic 5270 test instruments permit a flow range of 17–1760 mL/min. These devices are computer-controlled, allowing a static, cyclic, or intermittent deformation in a range of frequencies, amplitudes, and waveforms. The substrates used for culture plates of commercialized mechanical stimulation devices are typically flexible and light-transparent materials that enable phase-contrast, fluorescence, or scanning confocal microscopy analysis. The design and material choices allow, in some cases, simultaneous and real-time visualization using inverted microscopes. While these are often preferred to upright microscopes because they do not limit the total height of the device, it is mandatory to ensure that the focal length is not compromised. Despite the notorious progress on the tensile and compressive loading devices available on the market, the main motivation for research groups to design and fabricate their own devices is related to these device-associated costs. The cost of these devices ranges from thousands to tens of thousands of dollars, and the total price may increase when considering maintenance and the need to purchase additional device-specific accessories (such as culture well plates) in order to maximize the number of samples that can be tested at the same time [ 3 ]. Moreover, the macroscopic dimensions of some devices limit their throughput, and it is usually difficult or impossible to adapt to particular experiments such as, for example, using other substrate materials than polymers, which restricts the utility of these devices in a research context [ 3 , 51 , 52 , 72 ].

Custom-built cell-stimulation devices

Despite the focus on continuous innovation, mechanical stimulation systems available on the market present critical challenges. Consequently, numerous research groups have designed and developed custom-built devices to study the effects of tensile and compressive loading conditions on cellular behaviour.

Tensile loading devices

Several tensile loading devices with different designs and working principles have been developed in recent years. Table 3 lists uniaxial tensile loading studies in which devices were custom fabricated to meet research groups’ needs. The tensile loading working principles were divided into four major groups: four-point bending apparatuses, linear sliding rake systems, clamped samples connected to a tensile device, and vacuum-actuated tensile devices, as represented in Fig.  6 . The tensile loading devices designed by research groups are graphically arranged in Fig.  7 , according to the maximum strain/displacement and frequency under study.

Representation of four tensile working principles. In the four-point bending apparatus, the cell-based construct is supported by stationary supports and strain is distributed in the perpendicular plane to the applied load. However, the strain magnitude is not distributed uniformly between these horizontal planes because it increases from the central horizontal axis to the external medial and lateral faces (which are subjected to maximum tensile and compressive strains, respectively) [ 73 ]. Constructs can also be placed in cages and fixed at two opposite ends: one rigidly and the other to the rake attachment. The linear sliding rake is then controlled at the desired frequency and amplitude. Cell-based samples can also be clamped and connected to a tensile device (one end of the rectangular membrane is fixed while the other is connected to a computer-controlled movable frame). Finally, polymeric substrates may be exposed to uniaxial tensile loading with a vacuum-actuated tensile device. The movement imposed by the tensile loading device is represented by the red arrow

The majority of tensile loading devices involve cell culture on a circular flexible membrane (fixed along its periphery) or rectangular flexible membrane (fixed at opposite ends) (Fig.  7 ). Some of the results obtained by the studies mentioned in Table 3 are summarized in Fig.  8 .

Graphical arrangement of the devices designed and produced by research groups according to the maximum tensile strain/displacement studied at a particular frequency. Observation: despite the fact that Subramanian et al. [ 57 ] applied 2% uniaxial tensile strain to cells encapsulated in collagen constructs, the device used in this study may operate at a loading strain up to 12% at cyclic frequencies of 0.01–1 Hz

Results of studies performed with customized tensile loading devices. ALP staining at 24 h was higher for cells subjected to mechanical loading by a four-point bending device ( a ) compared to unstretched cells ( b ) and control cells ( c ) (reproduced from [ 43 ], Copyright 2008, with permission from Elsevier). d Scanning electron micrographs of 3D collagen constructs encapsulated with OB6, C2C12, or AC10 cells at day 3 either loaded by a linear sliding rake system or non-loaded (scale bar: 100 μm) indicated that the fibre orientation of loaded cells was parallel to the axis of load application (reproduced from [ 57 ], Copyright 2017, with permission from Wiley). e Staining of actin (green), sarcomeric z-lines (red), and nuclei (blue) of cardiomyocytes cultured on clamped samples connected to a tensile device revealed that after being subjected to 6 h of cyclic uniaxial tensile loading, the cells aligned in the direction of loading (white arrow) (reproduced from [ 3 ], Copyright 2018, with permission from ASME). f No significant differences in the average normalized total fluorescence of nuclei were found between non-stretched (control) and stretched groups, but F-actin fluorescence significantly increased with loading performed with a vacuum-actuated tensile device. The spatial distribution of per cent change between stretched and control average nuclei ( g ) and F-actin fluorescence ( h ) showed that expression of F-actin increased after tensile loading (reproduced from [ 52 ], Copyright 2018, with permission from Springer Science Business Media, LLC, part of Springer Nature)

Application of cyclic uniaxial (one direction) tensile strains sometimes leads to a heterogeneous biaxial strain profile, due to the Poisson effect. Therefore, custom-designed devices were developed to modulate equiaxial strains and generate a homogeneous strain environment [ 32 , 44 , 78 , 79 ]. Other groups focused on reproducing a more complex physiological environment by applying biaxial strains [ 80 , 81 ]. Tensile loading was also performed using piezoelectrically actuated pins of a Braille display [ 72 ]. Briefly, an elastomeric membrane of PDMS containing microwells was placed on top of an actuated pins array and deformed by the Braille pin movement. Each pin was independently computer-controlled and responsible for applying a cyclically radial strain (maximal 20%–25% radial and 12% tangential). Mouse myogenic C2C12 cells and human dermal microvascular endothelial cells (HDMECs) aligned to the loading direction at increasing frequencies of 0.2, 1, and 5 Hz, after 2, 4, and 12 h, in contrast to human lung adenocarcinoma epithelial A549 cells, which did not respond to tensile loading (Fig.  9 ) [ 72 ].

Schematic representation of the cross section of cells (represented in green) cultured on flexible membranes ( a ) and the deformation of the latter as the pin moves upwards ( b ). The alignment of C2C12 and HDMECs in response to loading is illustrated by fluorescent images of HDMECs ( c , d ), C2C12 myoblast cells ( e , f ), and A549 alveolar epithelial cells ( g , h ) stained with Calcein AM before loading (left column) and after being subjected to cyclical tensile loading (5 Hz for 12 h) (right column) (reproduced from [ 72 ], Copyright 2008, with permission from Elsevier). HDMECs: human dermal microvascular endothelial cells

Compressive loading devices

Microfabricated devices have been developed to apply compressive strain to cell-encapsulated constructs. Typically, the compression is achieved by loading pistons actuated by a pneumatic system. This type of compressive device can generate three types of compression: unconfined, semi-confined, and confined, all of which are illustrated in Fig.  10 .

Illustration of compression models: unconfined compression, confined compression, and semi-confined compression. The three-dimensional cell-based construct is compressed by the movement of a piston, in this case as a result of pressurized air (represented by the red arrow)

Unconfined compression was studied in the majority of compressive loading studies, as it represents the simplest microfabrication technique. One device was designed to study the influence of dynamic 10% compressive strain at 1 Hz for up to 3 weeks on chondrogenesis of goat bm-MSCs encapsulated in poly(ethylene glycol) diacrylate (PEGDA) hydrogels, as well as human embryonic body-derived (hEBd) cells encapsulated in tyrosine-glycine-aspartate-serine (YRGDS)-PEG-acrylate hydrogels [ 82 ]. The expression and synthesis of chondrocyte-specific matrix molecules were also studied, under the same loading conditions, with bovine bm-stromal cells encapsulated in agarose gels for 8 and 16 days [ 83 ]. Another group investigated the role of cyclical unconfined compression on osteogenesis by applying 10% and 20% compressive strains at 0.5 Hz for 4 h on rat pre-osteoblasts seeded into electrospun polycaprolactone (PCL) scaffolds [ 84 ]. Only the 10%-magnitude strain induced expression of osteogenic-related proteins and transcription factors, showing that elevated magnitudes may inhibit bone formation [ 84 ]. Ravichandran et al. designed a custom-fabricated device to apply a range of compressive strains to four independent chambers. hMSCs were seeded on polycaprolactone-β tricalcium phosphate (PCL-TCP) scaffolds using fibrin gel and then exposed to 0.22%, 0.88%, and 1.1% compressive strain at 1 Hz, 4 h/day for 4 weeks [ 85 ]. Cyclic physiological compression of 0.22% resulted in higher ALP activity compared to supra-physiological strains; it also up-regulated osteogenic markers and generated high mineralization levels [ 85 ]. C3H10T1/2 mouse MSCs were encapsulated in PEG hydrogels and exposed to 6%, 11%, 14%, and 26% compressive strains. Regardless of the strain magnitude, there was no significant difference in nuclear deformation, whereas cellular deformation only changed significantly at the highest strain levels [ 86 ]. The device proposed by Moraes et al. [ 86 ] consisted on an array of loading posts suspended over actuation cavities and was adopted and altered by Lee et al. to subject alginate-chondrocyte constructs to compressive strain [ 87 ]. These constructs were placed on PDMS balloons with different diameters and by varying only the cavity diameter (with the applied pressure remaining the same), it was possible to create a range of compressive strains. Because the balloons were inflated with pressurized air, compression on constructs was studied either in a static (14 kPa, 1 h) or dynamic (14 kPa, 1 Hz, 1 h) mode. Lee et al. found that the mean strain of chondrocytes was approximately 50% of the gel strain, with a permanent deformation of 9%–30% for static compression, and 0.5%–6% for dynamic compression. Finally, cell viability was found to be higher in dynamically loaded constructs, perhaps due to better nutrient transport [ 87 ]. Despite these findings, unconfined compression generates a heterogeneous strain distribution within the 3D construct. In contrast, confined compression generates a uniform strain, but challenges arise concerning its microfabrication. Semi-confined compression offers easier microfabrication, but uniform strains are only achieved in the central region of the biomaterial. These findings were obtained from the finite-element simulations (represented in Fig.  11 ), and the obtained strain fields for the three compression modes were compared [ 88 ].

Finite-element simulations of three compression modes all involved application of 10% compressive strain on PEG hydrogel (adapted from [ 88 ], Copyright 2011, with permission from IOP Publishing Ltd). Strain field within the hydrogel was generated for unconfined ( a ), confined ( b ), and semi-confined ( c ) compression modes and the radial, circumferential, and axial strains (mean and standard deviation) were plotted for the total axial thickness of the hydrogel

The same group fabricated a semi-confined compression device, which was used to generate nominal strains of 20%, 30%, 40%, and 45% on PEG and collagen hydrogels. The authors concluded that this compression model enables the study of cellular responses to precisely applied strains on a range of polymerizable biomaterials, improving the applicability and versatility of the device [ 88 ]. Zhang et al. [ 89 ] used a custom-designed dynamic-compression loading system with a stepper motor to apply a 10% compressive strain on PCL scaffolds encapsulated with hMSCs. PCL-based constructs subjected to both mechanical and biochemical stimulation supported a chondroprotective effect [ 89 ].

Review of patents

Given the promising outcomes from engineered mechanical stimulation devices in mechanobiology studies like those described above, many patent applications have been filed in the past few decades. We looked at both granted patents and patent applications, and conducted our research through the Derwent Innovation Index [ 90 ] and Google Patents [ 91 ] databases, which include European, USA, and World Patents (WIPO—World Intellectual Property Organization). The keywords were related to mechanical cell stimulation and resulted in a total of 369 records. We excluded inventions whose descriptions could not be automatically translated to English, those with unclear abstracts, and those not within the scope of this review.

A total of 44 patents of devices able to create different stimuli (tensile, compressive, shear stresses, and vibration) were comprehensively studied and selected, taking into account their in vitro cellular purposes. Table 4 summarizes the selected inventions. They are organized first by frequency level (low to moderate vs. high frequency), then by actuator type, as schematically illustrated in Fig.  12 , and finally by the imposed stress state. Inventions that obey non-conventional actuation principles are in a separate category.

Actuation principles of various mechanical cell-stimulation devices, divided by frequency level: low to high for values up to 200 Hz and extremely high frequency for values up to 100 MHz

To better organize the resulting inventions, we grouped them according to their actuation principle. From low to high frequencies, the actuation may be pneumatic (either positive or negative pressure), motor-driven, or magnetic. However, some inventors disclosed more than one functionality principle. The invention of Sittampalam et al. [ 96 ] is a drug-screening device and system that attempts to impart strain to cells in a similar manner to physiological motion and rest. According to their description, different mechanical drive systems can be adopted to move the pins and thus exert mechanical strain on cells, including a linear actuator (Fig.  13 a), an electromagnetic system, or a pneumatic system (Fig.  13 b).

The device of invention number US 2013/0059324 AI may be operated ( a ) by a mechanical drive mechanism, in which the rotation of a non-circular shaft (218) moves the movable support (216), thereby pushing the push members (214) in respect to the pins (118); or ( b ) by a pressurized mechanism (220), in which the change of fluid volume moves the support (216), imparting mechanical strain to the cells located in the wells (112). Illustrations from [ 96 ]

The device invented by Shapiro et al. [ 118 ], defined in Table 3 as belonging to the motor-driven category has, in fact, more than one approach to achieving membrane mechanical displacement (Fig.  14 ). The elastic membrane upon which the cell culture is placed is securely held in place and moved by a displacement applicator located, for example, on the bottom surface. Then, it is cyclically moved upward and downward by a force generator, deforming the membrane. This membrane deformation imparts biaxial forces (either tensile or compressive) to the cells mounted thereon, and the strain profile may be either uniform or non-uniform. The electric motor drives an actuating apparatus, such as a cam (Fig.  14 a), which revolves eccentrically about an axis, contacting the bottom surface of the rod and forcing the rod and displacement applicator to move upward to contact and deform the membrane. At the end of the upward stroke, the applicator moves to a lowered position out of contact with the membrane. The invention may also correspond to a mechanical actuated tensile apparatus which applies biaxial strain (Fig.  14 b) or simultaneously applies tensile loading to several cell cultures (Fig.  14 c). The removable and disposable wells are mounted above each available displacement applicator.

Illustrations of invention number US 5,348,879 of Shapiro et al., with three different displacement applicators (represented in the drawing by 24). In ( a ), a cam deforms the membrane, in ( b ), the membrane is secured by plates and is deformed by the displacement applicator moving upward, and in ( c ), each well is mounted above the displacement applicator. Schematics from [ 118 ]

Substrate deformation through the pneumatic actuation principle may be achieved by pressure [ 92 , 98 ] or vacuum [ 93 , 94 , 95 , 96 , 97 ], and by pulling a portion of the flexible membrane upward or downward, respectively. Despite the simple set-up, in both modes the stimulus frequency is low and may not even be capable of creating dynamic cycles. However, vacuum pumps are slower than pressure inlet. Other inventions aim to deform the membrane through pressurization of the fluid (e.g., culture medium) [ 99 , 102 ], or by creating hydrostatic pressure using a piston [ 100 ]. If not carefully designed, moving the flexible membrane upward through a displacement applicator, by pressure or manually (e.g. with a piston), may cause friction between the membrane of interest and the loading post of the device, as represented in Fig.  15 .

The displacement applicator moves up and down, which may create friction between the flexible membrane and the loading post

Hydraulic actuators are comprised of a hollow cylinder with a piston, and due to unbalanced pressure applied to the piston, a force is generated that deforms the membrane equiaxially. Although these actuators are often limited in terms of frequency, invention number DE102009057698A1 of Kiesow et al. [ 98 ] allows cyclic testing in a frequency range of 0.001 to 200 Hz.

Still, either in low- or high-frequency mode, the culture liquid in contact with the cells may be pressurized and the generated hydrostatic pressure then exerts a compressive mechanical force on cells.

The motor-driven mechanism involves the conversion of a rotary motion of an electric motor into linear displacement. The selected motor may be a stepper motor [ 103 , 104 , 106 , 107 , 108 , 109 , 110 , 111 , 117 ], a linear DC motor [ 105 , 113 , 114 , 119 , 128 ], a servo motor [ 126 ], or a voice-coil motor [ 105 , 115 ]. Stepper motors, which are composed of multiple toothed electromagnets, were preferred for some of these inventions. Despite the possibility of miniaturization, precise rotation (ranging from step angles through full 360° rotation), easy set-up and control, this type of motor is frequently slow due to a low transmission ratio (from rotational to linear movement). Moreover, it may cause small vibrations, which will act as an external disturbance to the system and thus should be considered separately from the substrate’s deformation. Linear DC motors are two-wire continuous rotation motors with each pulse being so fast that the motor seems to be rotating constantly with no stuttering. Servo motors are also fast, with high torque, and can be precisely controlled because of their accurate rotation within a limited angle. This actuation principle is particularly suitable for uniaxial tensile loading and for larger engineered constructs. In addition, it allows multiple loading modes and precise control over the strain features, such as amplitude and frequency. On the other hand, some potential disadvantages are the risk of contamination and limitation of high-throughput capabilities [ 134 ].

The linear actuation principle may be preferable because it allows for automation, requires less maintenance, and offers a broader range of strain magnitudes, frequencies, and durations of mechanical stimulus. Invention number US10,421,955B2, assigned to IonOptix LLC in 2019 (Fig.  16 ), applies a tensile strain up to 50% (at 0.01–10 Hz) on a deformable rectangular culture dish made, for example, from silicone rubber [ 111 ]. A plurality of viewing ports are provided to enable cell culture observation by microscope and exchange of the culture medium, permitting long-term experiments to be performed.

Illustrations of invention number US10,421,955B2, assigned to IonOptix LLC. ( a ) is a side view of the electromechanical stage (28a) composed by a fixed support (32) and a moving support (36) connected to a stepper motor (42). ( b ) is a perspective view illustrating six culture dishes and supporting parts of the electromechanical stage. Figures from [ 111 ]

Muthiah et al. [ 115 ] developed a mechanical tensile device, invention number US 2012/0219981Al, with dimensions of 408 mm×150 mm (much larger than a 24-well plate). It is composed of two engagement areas located at opposite ends of a flexible substrate; each one connected to a movable element and a motor to promote opposite movements, as shown in Fig.  17 . The device may include a temperature-control unit, such as a heating unit and/or a fan, to assure uniform distribution of heat and to maintain the temperature, a humidity reservoir unit, and a gas-control unit to control the gas parameters and supply. During or after tensile loading, the materials may also be imaged using a microscope base plate.

Schematics of invention number US 2012/0219981Al, assigned to Muthiah and Lane [ 115 ], in which each motor (denoted by 504 and 506) is connected to an opposite end of the cell culture device (502). The embodiment includes a water reservoir (512), an electric heating unit (508) and cooling fans (510), and computer interface connections (514). Figures from [ 115 ]

The magnetic actuation principle is an indirect method used to apply mechanical stresses on the substrate of interest. The actuating part is never in contact with the moveable one, which decreases the risk of contamination, but it is hard to control the strain and velocity. In addition, there is a potential unwanted magnetic effect on cells.

Looking further at low- to high-frequency range, some inventions apply fluid-flow-induced shear stress to cells. Despite the fact that this stimulus cannot be considered a mechanical cue for mechanotransduction studies given that it cannot be measured, Jiang et al.’s invention number CN10314657A also provides, according to the inventors, tensile stresses on cells [ 127 ], and Boronyak et al.’s invention number US 8,852,923 B2 may be adapted to impose cyclic flexural and/or tensile stresses [ 128 ].

The aforementioned inventions apply tensile, compressive, or shear stresses to cells, and some allow simultaneous electric stimulation. When cells are stimulated by deformation of the substrate on which they are cultured, those forces generate uniaxial, biaxial, or equiaxial strains (previously described in Fig.  3 ). In-plane substrate distension through frictionless platen displacement (by vacuum, pressure, or another means) creates biaxial strain traction on a flexible culture membrane and produces a uniform strain field [ 119 ]. This strain-profile output may be required for more accurate and controlled mechanotransduction studies, given that all cells cultured on the substrate are subjected to the same strain.

Actuation using piezoelectric or ultrasound elements was used to create vibration/oscillation. The main advantage is easy set-up, but the deformation created exhibits low amplitude and high frequency. In addition, the deformation of the piezo elements is not equal to the deformation of the substrate, and consequently of the cells, because losses are always present and, as the whole device vibrates, the vibrations can be even more attenuated.

Potential and future perspectives

Significant progress in research and technological fields has contributed to remarkable findings on the physiological dynamics of the human body. Basic life science research has moved from 2D culture systems to more complex 3D dynamic cultures, not only to improve cell culture conditions by promoting nutrient and oxygen flow to cells, but also to more closely mimic the complex physiological environment. Unlike bioreactors or microfluidic-based culture models, for the purpose of mechanobiology studies, cells are usually seeded on polymeric substrates or incorporated into 3D constructs and stimulated in mechanical force devices in order to investigate cell adaptation to different mechanical stresses, such as tensile or compressive stresses.

Regenerative medicine strategies involve the use of biomaterials whose mechanical properties and behaviour upon implantation may be studied in vitro by closely mimicking physiological conditions of, for example, bone [ 43 , 74 , 75 , 76 ], heart muscle [ 42 , 135 ], tendon [ 56 ], and lung [ 77 ]. By reproducing the physiological conditions to which the implants or biomaterials would be subjected, the need to perform in vivo animal testing would decrease. This would be in line with the European Directive 2010/63/EC which follows the “3Rs: reduction, refinement, and replacement” strategy to reinforce the importance of using alternative in vitro and in silico methods to obtain the maximal information from the intended product prior to clinical trials [ 136 , 137 , 138 ]. Despite more reliable studies conducted over the past years for multiple tissue-specific applications, there are still opportunities for further improvement. Mechanical stimulation devices should be designed (or integrated with other systems) to allow multiple and real-time assessment and evaluation of cell behaviour and responses at a microscale. One possibility is performing real-time imaging using non-invasive imaging techniques, fluorescence, or μCT. In order to assure optimal experimental conditions, mechanical stimulation devices could be coupled and assembled with sensors for monitor-based and cell-specific parameters, such as pH, temperature, oxygen, and secretion of small molecules and proteins.

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Acknowledgements

This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant SFRH/BD/141056/2018, the project PTDC/EME-EME/1442/2020 and under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020. In addition, this work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC).

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Melo-Fonseca, F., Carvalho, O., Gasik, M. et al. Mechanical stimulation devices for mechanobiology studies: a market, literature, and patents review. Bio-des. Manuf. 6 , 340–371 (2023). https://doi.org/10.1007/s42242-023-00232-8

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Challenging pitfalls in frozen section pathology: a case of mandible ghost cell odontogenic carcinoma and the literature review

• Sha-Sha Hu 1   na1 ,
• Jian Yang 2   na1 ,
• Hai-Fei Zhang 1   na1 ,
• Jie Chen 1 ,
• Xin-Nian Li 1 ,
• Fu-Jin Liu 1 &
• Bo Wang 1  

BMC Oral Health volume  24 , Article number:  450 ( 2024 ) Cite this article

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Ghost cell odontogenic carcinoma (GCOC) is a rare malignancy characterized by the presence of ghost cells, preferably in the maxilla. Only slightly more than 50 case reports of GCOC have been documented to date. Due to the rarity of this tumor and its nonspecific clinical criteria, there is a heightened risk of misdiagnosis in clinical examination, imaging findings, and pathology interpretation.

Case presentation

A 50-year-old male patient presented to the hospital due to experiencing pain in his lower front teeth while eating for the past 2 months. Upon examination, a red, hard, painless mass was found in his left lower jaw, measuring approximately 4.0 cm × 3.5 cm. Based on the malignant histological morphology of the tumor and the abundant red-stained keratinized material, the preoperative frozen section pathology misdiagnosed it as squamous cell carcinoma (SCC). The surgical resection specimen pathology via paraffin section revealed that the tumor was characterized by round-like epithelial islands within the fibrous interstitium, accompanied by a large number of ghost cells and some dysplastic dentin with infiltrative growth. The malignant components displayed marked heterogeneity and mitotic activity. Additionally, a calcified cystic tumor component of odontogenic origin was observed. Hemorrhage, necrosis, and calcifications were present, with a foreign body reaction around ghost cells. Immunoreactivity for β-catenin showed strong nuclear positivity in tumor cells, while immunostaining was completely negative for p53. The Ki67 proliferation index was approximately 30–40%. The tumor cells exhibited diffuse CK5/6, p63, and p40 immunoreactivity, with varying immunopositivity for EMA. Furthermore, no BRAF V600E mutation was identified by ARMS-PCR. The final pathology confirmed that the tumor was a mandible GCOC.

We have reported and summarized for the first time the specific manifestations of GCOC in frozen section pathology and possible pitfalls in misdiagnosis. We also reviewed and summarized the etiology, pathological features, molecular characteristics, differential diagnosis, imaging features, and current main treatment options for GCOC. Due to its rarity, the diagnosis and treatment of this disease still face certain challenges. A correct understanding of the pathological morphology of GCOC, distinguishing the ghost cells and the secondary stromal reaction around them, is crucial for reducing misdiagnosis rates.

Peer Review reports

Ghost cell odontogenic carcinoma (GCOC) is a very rare malignancy originating from odontogenic epithelium, typically affecting patients aged from 40 to 70 years, with a higher occurrence in males [ 1 ]. GCOC, characterized by poorly demarcated lesion radiologically, ameloblastoma-like epithelium, prominent ghost cells and cytological evidence of malignancy, is about the rarest of the ghost cell lesions, accounting for approximately 0.23% of all odontogenic tumors and less than 3% of all ghost cell lesions [ 1 , 2 , 3 ]. In 2005, it was included in the World Health Organization (WHO) classification of malignant odontogenic tumors [ 4 ]. Since Ikemura et al. firstly recorded a case in detail in 1985 [ 5 ], only slightly more than 50 case reports of GCOC have been documented to date [ 6 ]. About 55% cases of GCOC are thought to originate from de novo, others arise from pre-existing calcifying odontogenic cyst (COC) or dentinogenic ghost cell tumor (DGCT) [ 7 ]. These three tumors manifest similar clinical and radiological features, making the diagnosis challenging. Given the rarity and nonspecific clinical criteria of the tumor, clinical examination, imaging findings and pathology are also prone to misdiagnosis.

Here, we report a rare case of mandible ghost cell odontogenic carcinoma that was misdiagnosed as squamous cell carcinoma on intraoperative incisional biopsy frozen section pathology.

In April 2021, a 50-year-old male patient presented to the hospital with complaints of painful feeling while eating in his lower anterior teeth for 2 months. His examination revealed a red, hard, painless swelling of approximately 4.0 cm × 3.5 cm in size, located in the left mandible. The patient exhibited poor overall oral hygiene, and his teeth had grade II mobility with caries. However, no enlargement of the lymph nodes in the lower jaw or the oral cavity was detected. The rest of the dental specialty examination revealed no abnormalities. This patient had a long-term betel nut chewing habit and no other genetic or chronic diseases. The attending physician at the time diagnosed a mandibular cyst. Maxillofacial computerized tomogram (CT) suggested a soft tissue mass with bone destruction in the median alveolar region of the mandible (Fig.  1 A-C), which was considered a tumorigenic lesion. Postoperative CT showed no residual mass (Fig.  1 D).

Preoperative CT and intraoperative pathologic frozen examination. ( A , B ) Computed tomography (CT) showed a soft tissue mass with bone destruction in the mandible (red arrows). ( C ) 3D reconstruction of CT scan showed significant loss in the median alveolar region of the mandible with no signs of fracture ( D ) Postoperative images. ( E , F ) In frozen section pathology, resected tumor showed variable patterns of solid nests or cords. ( G , H ) The tumor cells with pleomorphism, increased N/C ratio, nuclear hyperchromatism, and mitotic activity. ( I ) There were large numbers of homogeneous red-stained unstructured or hyaline stroma similar to keratinization. ( J ) Foreign body granuloma reaction could be seen in the surrounding interstitium (red arrows).

The initial frozen biopsy section examination displayed the lesion dominated by large numbers of homogeneous red-stained unstructured or hyaline stroma, resembling keratinization (Fig. 1I). Scattered among these stromal elements were tumor cells exhibiting pleomorphism, increased nuclear/cytoplasmic (N/C) ratio, nuclear hyperchromatism, and mitotic activity (Fig.  1 G, H). The tumor cells formed solid nests or cords (Fig.  1 E, F), indicative of a malignant epithelial tumor. Additionally, a foreign body granuloma reaction was observed in the surrounding interstitium (Fig.  1 J). In conclusion, the final frozen section pathology diagnosis was SCC.

Upon admission, the patient was initially suspected to have a mandibular cyst. However, intraoperative freezing indicated the presence of squamous cell carcinoma in the mandibular mass. Considering the significant shift in the tumor’s nature, the medical team made the decision to modify the initially planned surgical approach and broaden the extent of the procedure after consulting with the patient’s family. The revised surgical approach consisted of several steps. First, a partial resection of the mandible and the mass was performed. This was followed by bilateral cervical lymphadenectomy to remove any potentially affected lymph nodes. The next step involved repairing the defect in the fundus. To reconstruct the area, an excision was performed, and a vascularized free peroneal myocutaneous flap was used as a graft. A small arterial anastomosis was then carried out to ensure proper blood supply to the graft. Solid internal fixation was applied to stabilize the mandible. Additionally, the fibula, along with its blood vessels, was extracted for further reconstruction purposes. Finally, a tracheotomy was performed. These modifications to the surgical procedure were made in order to effectively address the presence of squamous cell carcinoma and ensure the best possible outcome for the patient.

The treatment involved excision of part of the mandibular bone and mass. Grossly, surgical specimen measured 6.5 × 5.5 × 4.0 cm, with 5 teeth attached to it. The area of alveolar mucosa showed an ulcerated mass (Fig.  2 A). The cut surface of the tumor was 2.2 × 1.3 × 2.1 cm in diameter, presented as a gray to taupe solid mass with areas of hemorrhage and cystic change and invaded the mandible (Fig.  2 B).

Postoperative pathology analysis. ( A , B ) Gross excision specimen and tumor incision surface (red circles). ( C ) Microscopically, paraffin section showed the tumor boundary was not clear. ( D , E ) Hematoxylin and eosin stain (HE) showed that tumor cells are arranged in solid nests and anastomosing cords. ( F , G ) The tumor was composed of small cells with hyperchromatic nuclei or large cells with vacuolated nuclei, with marked heterogeneity and mitotic activity (red arrows). ( H , I ) A calcified cystic tumor component of odontogenic origin could be seen and the malignant epithelial component were separated from or mixed with the benign lesion. (J-O) Ghost cells ( J ), dentinoid material ( K ), hemorrhage ( L ), necrosis ( M ) and calcifications ( N ) could be found, with foreign body reaction around ghost cell ( O ).

The histological examination revealed the tumor was characterized by round-like epithelial islands within the fibrous interstitium, accompanied by a large numbers of ghost cells and a little dysplastic dentin with infiltrative growth (Fig.  2 C). Histopathological sections revealed solid nests and anastomosing cords (Fig.  2 D, E). The malignant components consisted of round-like epithelial islands, with some cells appearing as small round cells with deeply stained nuclei, while others exhibited large cells with vacuolated nuclei, displaying marked heterogeneity and mitotic activity (Fig.  2 F, G). A calcified cystic tumor component of odontogenic origin could be seen. The malignant epithelial component was observed either separated from or mixed with the benign lesion (Fig.  2 H, I). The ghost cells were round or ovoid, with red-stained cytoplasm, disappearing uncolored nuclei, and empty bright areas at the nuclei (Fig.  2 J). Dentinoid material and hemorrhage, necrosis and calcifications could be found, with foreign body reaction around ghost cell (Fig.  2 K-O).

An extensive immunohistochemical panel was performed. Immunoreactivity for β-catenin showed strong nuclear positivity in tumor cells. Immunostaining was completely negative for p53. The Ki67 proliferation index was around 30–40%. The tumor cells showed diffuse CK5/6, p63 and p40 immunoreactivity. There was varying immunopositivity for EMA. Immunostaining was negative for Vimentin (Vim), S-100, Synaptophysin (Syn) and Chromogranin A (CgA) (Fig.  3 ). No BRAF V600E mutation was identified by amplification refractory mutation system polymerase chain reaction (ARMS-PCR).

Immunohistochemistry showed expression of CK5/6, p63, Vim, β-catenin, p53 and Ki67.

The final pathology via paraffin section showed that the tumor was a mandible GCOC. We reviewed and summarized the possible pitfalls of frozen section pathology diagnosis of GCOC. A large numbers of ghost cells could be seen between the tumor cells of GCOC, and there was no intercellular bridge between cells (Fig.  4 A, B). The homogeneous red-stained unstructured materials were very characteristic ghost cells (Fig.  4 C), and a little dentin material could be found by careful observation (Fig.  4 D). In addition, calcifications (Fig.  4 E) and foreign body granuloma reaction (Fig.  4 F) around ghost cells were also suggestive for the diagnosis of GCOC.

The possible pitfalls of frozen section pathology diagnosis of GCOC. ( A ) A large number of ghost cells could be seen, ( B ) There was no intercellular bridge between cells. ( C ) The homogeneous red-stained unstructured materials were very characteristic ghost cells. ( D - E ) A little dentin material ( D ), calcifications ( E ) and foreign body granuloma reaction around ghost cells ( F ) could be found by careful observation.

The patient finally recovered and was discharged in May 2021. Under the strict regular physical and imaging examinations, the patient has no signs of tumor recurrence within two years of follow-up. Patients gave their affirmation and adequate cooperation to the process and results of treatment.

This report described a rare case of mandibular GCOC that was misdiagnosed as SCC by frozen section pathology during the perioperative period. Previous examinations and imaging findings were inconclusive. Intraoperative frozen section pathology was diagnosed as SCC on the basis of cytological evidence of malignancy and a large number of keratin-like red-stained unstructured structures. Until the final paraffin section pathology corrects the diagnosis as GCOC.

GCOC is an extremely rare destructive and aggressive malignant odontogenic tumor. Due to its different histopathological features, various terms have been used to define the disease, including calcifying ghost cell odontogenic carcinoma, aggressive epithelial ghost cell odontogenic tumors, malignant epithelial odontogenic ghost cell tumor, carcinoma arising in a calcifying odontogenic cyst, malignant calcifying ghost cell odontogenic tumors and malignant calcifying odontogenic cyst [ 8 , 9 ]. So far, only more than 50 cases have been reported in the English literature, with about 40% of the cases occurring in Asian patients [ 6 ]. GCOC has a male predominance, occurring in individuals from 3 to 92 years [ 10 ]. In one study, it was suggested that GCOC was twice as common in the maxilla as in the mandible [ 8 ]. Another statistical survey showed that GCOC occurred more frequently in the maxilla than in the mandible, with 31 out of 51 patients occurring in the maxilla [ 11 ]. These tumors have been intraosseous and mandibular lesions are usually in the molar area [ 12 ]. Given the rarity of the disease and the non-specificity of its clinical features, little is known about GCOC. Therefore, the progression of GCOC is unpredictable. Meanwhile, it may vary from slow progression to rapid destructive behavior, with recurrence and occasional distant metastasis to axillary skin, brain, and lung [ 13 ].

The diagnosis of GCOC is challenging and difficult for the first attending physician, and even pathologists face a high risk of misdiagnosis due to its rarity, complexity and inexperience. In imaging, GCOC does not have specific imaging features, so pathological testing remains the primary and most important way to identify. For the differential diagnosis of GCOC, the main differentiators are benign odontogenic tumors, dentinogenic ghost cell tumor (DGCT), calcifying odontogenic cyst/ calcifying cystic odontogenic tumor (COC/ CCOT), odontomas, cholesterol granuloma of the maxillary sinus (CGMS), amelobalstoma and also in craniopharyngiomas and pilomatricomas [ 14 ]. In addition, if ghost cells are not present in the frozen section, the possibility of ameloblastic carcinoma should also be considered. Generally benign lesions tend to have well-defined margins, while malignant tumors are mostly destructive and ill-defined [ 15 ]. WHO describes the DGCT parenchyma as presenting an ameloblastomatous proliferation with occasional significant component of hyperchromatic basaloid cells [ 16 ]. Exuberant areas with spindle-shaped cells and sieve-like structures can also be observed in some cases [ 17 ]. However, one must be alert to the fact that while ameloblastomas and sieve patterns can be found in other odontogenic lesions such as ameloblastomas and adenoid ameloblastomas, these lesions may also have scattered ghost cells [ 18 ]. CGMS is characterized by a large number of cholesterol clefts surrounded by multinucleated giant cells, histiocytes, plasma cells, lymphocytes, and hemosiderin deposits [ 19 , 20 ]. CCOT is characterized by proliferation of odontogenic epithelium and scattered nests of ghost cells and calcifications that may form the lining of a cyst, or present as a solid mass [ 21 ]. COCs are recognized by cystic proliferation with a fibrous capsule. The thickness of lining epithelium may vary between 4 and 10 layers. Areas of calcification and ghost cells can be observed [ 22 ].

In our case, the frozen section pathology was misdiagnosed as SCC. If the pathologist has insufficient diagnostic experience and encounters challenges like easy deformation and poor staining of frozen pathological sections, there is a risk of mistaking ghost cells for keratinized cells without careful identification. Therefore, distinguishing GCOC from well-differentiated SCC is crucial. Reviewing our cases and the pathological features of the two tumors, we summarize the following points of differentiation: (1) GCOC is sometimes secondary to COC or DGCT with mixed or segregated benign epithelial components and malignant epithelial components, which can be seen in our paraffin section pathology; whereas SCC can be seen with varying degrees of squamous intraepithelial lesions. (2) GCOC shows ameloblastoma-like epithelium with fenestrated peripheral cells in the cell nest, a typical structure not seen in our case, while basal cell-like SCC shows fenestrated peripheral cells in the cell nest. (3) In GCOC, a large numbers of ghost cells were seen around the nest and anastomotic strips, i.e., round or ovoid cells with red-stained cytoplasm and absent, uncolored nuclei, and empty bright areas in the nuclei; a large number of keratinized cells were seen in the center of the nest of well-differentiated SCC cells and formed keratinized beads. GCOC keratinization differs from normal keratinization in several aspects. Firstly, GCOCs are larger than keratotic squames. Secondly, they are often vacuolated, containing small fluid-filled spaces. Lastly, GCOCs exhibit prominent remnants of the nuclear membrane [ 23 ]. Failure to correctly identify ghost cells is also a major cause of misdiagnosis in our frozen section pathology. (4) GCOC consists of small cells with deeply stained nuclei or large cells with vacuolated nuclei and basophilic cells; well-differentiated SCC cells are large with eosinophilic or biphilic cytoplasm and intercellular bridges are seen. (5) In addition, consistent with what has been reported in other literature, the presence of dentin as well as calcification and foreign body granulomatous reaction in the ghost cell area can help to identify GCOC [ 10 , 23 ], and after careful observation, these lesions are seen in our frozen pathological sections.

The etiology of GCOC is controversial, and current pathogenesis theories include: GCOC occurs secondary to calcifying cystic odontogenic tumors [ 24 ]; GCOC is caused by dentinogenic ghost cell tumors [ 20 ]; de novo, with no previous associated lesions [ 25 , 26 ]; genetic mutations are a possible direction [ 7 ]. Rappaport et al. reported that mutation of the β-catenin gene was noted at codon 33 in GCOC [ 27 ]. Three other genomic alterations in GCOC: CTNNB1 S33C, CREBBP K1741* and MLL2 S1997fs*44 [ 27 ]. An extensive integrative genomic and transcriptomic analysis of GCOC studied by Bose et al. reported numerous genomic alterations [ 28 ]. P53 overexpression and UBR5 mutations were also reported in the GCOC [ 29 ], while in another study genetic abnormalities were found in NOTCH1 and PTEN due to deletion [ 18 ]. However, one must be alert to the fact that while ameloblastomatous and cribriform patterns can be found in other odontogenic lesions such as ameloblastoma and adenoid ameloblastoma, these lesions may also have scattered ghost cells [ 16 , 30 ]. In our case, immunohistochemical results showed a positive β-catenin diffuse nucleus with complete deletion of p53 expression and showed a high proliferation index of ki-67. We used ARMS-PCR to detect BRAF V600E , but the test result was negative.

Due to the extreme scarcity of cases, there is still considerable disagreement among different authors regarding the prevalent location of GCOC, its metastatic characteristics, and treatment options. Currently, more researchers believe that the main site of predilection for GCOC is the maxilla, and the most common clinical symptom is a painful swelling of the upper jaw accompanied by local sensory abnormalities [ 31 ]. The most typical radiological features of GCOC show a mixed pattern of radiolucent and radiopaque lesions with ill-defined borders, with or without root resorption and tooth displacement [ 31 , 32 ]. However, in this case, the boundaries of GCOC are well defined, and the rare morbidity and atypical imaging pattern are more likely to lead to an error in the initial clinical diagnosis, making the pathological diagnosis of GCOC extremely important. The current GCOC recommended treatment is extensive surgical excision of at least 5 mm of free margin with no residual outside the incision margin [ 33 ]. The most frequent procedures include marginal, segmental or partial resection or total maxillectomy, depending on the size of the lesions [ 32 , 34 ]. Post-surgical treatment options include adjuvant chemotherapy, adjuvant immunotherapy, and adjuvant radiotherapy, but the effectiveness of treatment remains controversial to this day. Qin Y, et al. reported significant symptom improvement in patient who underwent extensive surgery followed by two cycles of chemotherapy and radiotherapy, along with four rounds of weekly chemotherapy [ 20 ]. However, some researchers have pointed out that the benefit of adjuvant radiotherapy for GCOC patients is difficult to determine [ 24 , 26 ]. In 2015, Ahmed et al. reported the first case treated successfully with aggressive multimodal therapy in a 10 year old patient with regional lymph node metastasis that included surgery, adjuvant chemoradiation, and adjuvant immunotherapy [ 35 ]. Lu Y et al. reported that the 5-year survival rate of GCOC was about 73% [ 36 ]. In another related paper, the recurrence rate for recurrence, metastasis, and survival in GCOC was reported to be 63.4% [ 32 ]. Due to the limited number of cases and high recurrence rate, our knowledge of GCOC is limited, and prognosis is difficult to predict. Therefore, long-term follow-up and monitoring are necessary.

Conclusions

We report a highly unusual case of GCOC, initially misdiagnosed as SCC on frozen section pathology, and subsequently diagnosed as GCOC through a series of pathologic examinations. GCOC has been poorly studied due to its nonspecific clinical features and extremely low incidence, especially since frozen section pathology reports have never been reported. At the same time, we summarized the clinical features, imaging characteristics and treatment options of GCOC. Our report presents, for the first time, the pathological presentation of GCOC through frozen section pathology, along with a thorough analysis of potential misdiagnosis pitfalls for more pathologists, in order to deepen their understanding of this disease and reduce the misdiagnosis rate of intraoperative freezing. This case provides valuable and informative data and insights, contributing to our understanding of this rare entity with limited reported cases.

Data availability

All data generated or analysed during this study are included in this published article.

Abbreviations

• Ghost cell odontogenic carcinoma

squamous cell carcinoma

calcifying cystic odontogenic tumor

calcifying odontogenic cyst

dentinogenic ghost cell tumor

computerized tomogram

amplification refractory mutation system polymerase chain reaction

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Acknowledgements

We thank the Pathology Committee of Hainan General Hospital for their assistance and helpful suggestions.

This work was supported by Hainan Provincial Natural Science Foundation of China (820QN387), Hainan Province Science and Technology Special Fund of China (ZDKJ2021040, ZDYF2021SHFZ247), Clinical Translational Innovation Cultivating Fund 550 Project of Hainan General Hospital (2021CXZH02), National Natural Science Fund Cultivating 530 Project of Hainan General Hospital (2021MSXM13) and Joint Program on Health Science & Technology Innovation of Hainan Province (WSJK2024QN013).

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Sha-Sha Hu, Jian Yang and Hai-Fei Zhang are co-first authors.

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Department of Pathology, Hainan General Hospital (Hainan Affiliated Hospital of Hainan Medical University), Haikou, 570311, China

Sha-Sha Hu, Hai-Fei Zhang, Jie Chen, Xin-Nian Li, Fu-Jin Liu & Bo Wang

Department of Wound Repair, The First Affiliated Hospital of Hainan Medical University, Hainan Medical University, Haikou, 570311, China

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SH and JY handled the case and drafted the manuscript. FZ and JC assisted in the collection of case information and literature and did all the documentation and article work. XL, FL and BW put great effort and made many constructive comments during the revision and writing of this article. SH and BW acquired funding, provided resources and supervised all the work. All authors contributed to the review and editing process. All authors approved the final work.

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Hu, SS., Yang, J., Zhang, HF. et al. Challenging pitfalls in frozen section pathology: a case of mandible ghost cell odontogenic carcinoma and the literature review. BMC Oral Health 24 , 450 (2024). https://doi.org/10.1186/s12903-024-04190-0

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Received : 12 November 2023

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DOI : https://doi.org/10.1186/s12903-024-04190-0

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