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6.1 Experiment Basics

Learning objectives.

• Explain what an experiment is and recognize examples of studies that are experiments and studies that are not experiments.
• Explain what internal validity is and why experiments are considered to be high in internal validity.
• Explain what external validity is and evaluate studies in terms of their external validity.
• Distinguish between the manipulation of the independent variable and control of extraneous variables and explain the importance of each.
• Recognize examples of confounding variables and explain how they affect the internal validity of a study.

What Is an Experiment?

As we saw earlier in the book, an experiment is a type of study designed specifically to answer the question of whether there is a causal relationship between two variables. Do changes in an independent variable cause changes in a dependent variable? Experiments have two fundamental features. The first is that the researchers manipulate, or systematically vary, the level of the independent variable. The different levels of the independent variable are called conditions. For example, in Darley and Latané’s experiment, the independent variable was the number of witnesses that participants believed to be present. The researchers manipulated this independent variable by telling participants that there were either one, two, or five other students involved in the discussion, thereby creating three conditions. The second fundamental feature of an experiment is that the researcher controls, or minimizes the variability in, variables other than the independent and dependent variable. These other variables are called extraneous variables. Darley and Latané tested all their participants in the same room, exposed them to the same emergency situation, and so on. They also randomly assigned their participants to conditions so that the three groups would be similar to each other to begin with. Notice that although the words manipulation and control have similar meanings in everyday language, researchers make a clear distinction between them. They manipulate the independent variable by systematically changing its levels and control other variables by holding them constant.

Internal and External Validity

Internal validity.

Recall that the fact that two variables are statistically related does not necessarily mean that one causes the other. “Correlation does not imply causation.” For example, if it were the case that people who exercise regularly are happier than people who do not exercise regularly, this would not necessarily mean that exercising increases people’s happiness. It could mean instead that greater happiness causes people to exercise (the directionality problem) or that something like better physical health causes people to exercise and be happier (the third-variable problem).

The purpose of an experiment, however, is to show that two variables are statistically related and to do so in a way that supports the conclusion that the independent variable caused any observed differences in the dependent variable. The basic logic is this: If the researcher creates two or more highly similar conditions and then manipulates the independent variable to produce just one difference between them, then any later difference between the conditions must have been caused by the independent variable. For example, because the only difference between Darley and Latané’s conditions was the number of students that participants believed to be involved in the discussion, this must have been responsible for differences in helping between the conditions.

An empirical study is said to be high in internal validity if the way it was conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Thus experiments are high in internal validity because the way they are conducted—with the manipulation of the independent variable and the control of extraneous variables—provides strong support for causal conclusions.

External Validity

At the same time, the way that experiments are conducted sometimes leads to a different kind of criticism. Specifically, the need to manipulate the independent variable and control extraneous variables means that experiments are often conducted under conditions that seem artificial or unlike “real life” (Stanovich, 2010). In many psychology experiments, the participants are all college undergraduates and come to a classroom or laboratory to fill out a series of paper-and-pencil questionnaires or to perform a carefully designed computerized task. Consider, for example, an experiment in which researcher Barbara Fredrickson and her colleagues had college students come to a laboratory on campus and complete a math test while wearing a swimsuit (Fredrickson, Roberts, Noll, Quinn, & Twenge, 1998). At first, this might seem silly. When will college students ever have to complete math tests in their swimsuits outside of this experiment?

The issue we are confronting is that of external validity. An empirical study is high in external validity if the way it was conducted supports generalizing the results to people and situations beyond those actually studied. As a general rule, studies are higher in external validity when the participants and the situation studied are similar to those that the researchers want to generalize to. Imagine, for example, that a group of researchers is interested in how shoppers in large grocery stores are affected by whether breakfast cereal is packaged in yellow or purple boxes. Their study would be high in external validity if they studied the decisions of ordinary people doing their weekly shopping in a real grocery store. If the shoppers bought much more cereal in purple boxes, the researchers would be fairly confident that this would be true for other shoppers in other stores. Their study would be relatively low in external validity, however, if they studied a sample of college students in a laboratory at a selective college who merely judged the appeal of various colors presented on a computer screen. If the students judged purple to be more appealing than yellow, the researchers would not be very confident that this is relevant to grocery shoppers’ cereal-buying decisions.

We should be careful, however, not to draw the blanket conclusion that experiments are low in external validity. One reason is that experiments need not seem artificial. Consider that Darley and Latané’s experiment provided a reasonably good simulation of a real emergency situation. Or consider field experiments that are conducted entirely outside the laboratory. In one such experiment, Robert Cialdini and his colleagues studied whether hotel guests choose to reuse their towels for a second day as opposed to having them washed as a way of conserving water and energy (Cialdini, 2005). These researchers manipulated the message on a card left in a large sample of hotel rooms. One version of the message emphasized showing respect for the environment, another emphasized that the hotel would donate a portion of their savings to an environmental cause, and a third emphasized that most hotel guests choose to reuse their towels. The result was that guests who received the message that most hotel guests choose to reuse their towels reused their own towels substantially more often than guests receiving either of the other two messages. Given the way they conducted their study, it seems very likely that their result would hold true for other guests in other hotels.

A second reason not to draw the blanket conclusion that experiments are low in external validity is that they are often conducted to learn about psychological processes that are likely to operate in a variety of people and situations. Let us return to the experiment by Fredrickson and colleagues. They found that the women in their study, but not the men, performed worse on the math test when they were wearing swimsuits. They argued that this was due to women’s greater tendency to objectify themselves—to think about themselves from the perspective of an outside observer—which diverts their attention away from other tasks. They argued, furthermore, that this process of self-objectification and its effect on attention is likely to operate in a variety of women and situations—even if none of them ever finds herself taking a math test in her swimsuit.

Manipulation of the Independent Variable

Again, to manipulate an independent variable means to change its level systematically so that different groups of participants are exposed to different levels of that variable, or the same group of participants is exposed to different levels at different times. For example, to see whether expressive writing affects people’s health, a researcher might instruct some participants to write about traumatic experiences and others to write about neutral experiences. The different levels of the independent variable are referred to as conditions , and researchers often give the conditions short descriptive names to make it easy to talk and write about them. In this case, the conditions might be called the “traumatic condition” and the “neutral condition.”

Notice that the manipulation of an independent variable must involve the active intervention of the researcher. Comparing groups of people who differ on the independent variable before the study begins is not the same as manipulating that variable. For example, a researcher who compares the health of people who already keep a journal with the health of people who do not keep a journal has not manipulated this variable and therefore not conducted an experiment. This is important because groups that already differ in one way at the beginning of a study are likely to differ in other ways too. For example, people who choose to keep journals might also be more conscientious, more introverted, or less stressed than people who do not. Therefore, any observed difference between the two groups in terms of their health might have been caused by whether or not they keep a journal, or it might have been caused by any of the other differences between people who do and do not keep journals. Thus the active manipulation of the independent variable is crucial for eliminating the third-variable problem.

Of course, there are many situations in which the independent variable cannot be manipulated for practical or ethical reasons and therefore an experiment is not possible. For example, whether or not people have a significant early illness experience cannot be manipulated, making it impossible to do an experiment on the effect of early illness experiences on the development of hypochondriasis. This does not mean it is impossible to study the relationship between early illness experiences and hypochondriasis—only that it must be done using nonexperimental approaches. We will discuss this in detail later in the book.

In many experiments, the independent variable is a construct that can only be manipulated indirectly. For example, a researcher might try to manipulate participants’ stress levels indirectly by telling some of them that they have five minutes to prepare a short speech that they will then have to give to an audience of other participants. In such situations, researchers often include a manipulation check in their procedure. A manipulation check is a separate measure of the construct the researcher is trying to manipulate. For example, researchers trying to manipulate participants’ stress levels might give them a paper-and-pencil stress questionnaire or take their blood pressure—perhaps right after the manipulation or at the end of the procedure—to verify that they successfully manipulated this variable.

Control of Extraneous Variables

An extraneous variable is anything that varies in the context of a study other than the independent and dependent variables. In an experiment on the effect of expressive writing on health, for example, extraneous variables would include participant variables (individual differences) such as their writing ability, their diet, and their shoe size. They would also include situation or task variables such as the time of day when participants write, whether they write by hand or on a computer, and the weather. Extraneous variables pose a problem because many of them are likely to have some effect on the dependent variable. For example, participants’ health will be affected by many things other than whether or not they engage in expressive writing. This can make it difficult to separate the effect of the independent variable from the effects of the extraneous variables, which is why it is important to control extraneous variables by holding them constant.

Extraneous Variables as “Noise”

Extraneous variables make it difficult to detect the effect of the independent variable in two ways. One is by adding variability or “noise” to the data. Imagine a simple experiment on the effect of mood (happy vs. sad) on the number of happy childhood events people are able to recall. Participants are put into a negative or positive mood (by showing them a happy or sad video clip) and then asked to recall as many happy childhood events as they can. The two leftmost columns of Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” show what the data might look like if there were no extraneous variables and the number of happy childhood events participants recalled was affected only by their moods. Every participant in the happy mood condition recalled exactly four happy childhood events, and every participant in the sad mood condition recalled exactly three. The effect of mood here is quite obvious. In reality, however, the data would probably look more like those in the two rightmost columns of Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” . Even in the happy mood condition, some participants would recall fewer happy memories because they have fewer to draw on, use less effective strategies, or are less motivated. And even in the sad mood condition, some participants would recall more happy childhood memories because they have more happy memories to draw on, they use more effective recall strategies, or they are more motivated. Although the mean difference between the two groups is the same as in the idealized data, this difference is much less obvious in the context of the greater variability in the data. Thus one reason researchers try to control extraneous variables is so their data look more like the idealized data in Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” , which makes the effect of the independent variable is easier to detect (although real data never look quite that good).

Table 6.1 Hypothetical Noiseless Data and Realistic Noisy Data

One way to control extraneous variables is to hold them constant. This can mean holding situation or task variables constant by testing all participants in the same location, giving them identical instructions, treating them in the same way, and so on. It can also mean holding participant variables constant. For example, many studies of language limit participants to right-handed people, who generally have their language areas isolated in their left cerebral hemispheres. Left-handed people are more likely to have their language areas isolated in their right cerebral hemispheres or distributed across both hemispheres, which can change the way they process language and thereby add noise to the data.

In principle, researchers can control extraneous variables by limiting participants to one very specific category of person, such as 20-year-old, straight, female, right-handed, sophomore psychology majors. The obvious downside to this approach is that it would lower the external validity of the study—in particular, the extent to which the results can be generalized beyond the people actually studied. For example, it might be unclear whether results obtained with a sample of younger straight women would apply to older gay men. In many situations, the advantages of a diverse sample outweigh the reduction in noise achieved by a homogeneous one.

Extraneous Variables as Confounding Variables

The second way that extraneous variables can make it difficult to detect the effect of the independent variable is by becoming confounding variables. A confounding variable is an extraneous variable that differs on average across levels of the independent variable. For example, in almost all experiments, participants’ intelligence quotients (IQs) will be an extraneous variable. But as long as there are participants with lower and higher IQs at each level of the independent variable so that the average IQ is roughly equal, then this variation is probably acceptable (and may even be desirable). What would be bad, however, would be for participants at one level of the independent variable to have substantially lower IQs on average and participants at another level to have substantially higher IQs on average. In this case, IQ would be a confounding variable.

To confound means to confuse, and this is exactly what confounding variables do. Because they differ across conditions—just like the independent variable—they provide an alternative explanation for any observed difference in the dependent variable. Figure 6.1 “Hypothetical Results From a Study on the Effect of Mood on Memory” shows the results of a hypothetical study, in which participants in a positive mood condition scored higher on a memory task than participants in a negative mood condition. But if IQ is a confounding variable—with participants in the positive mood condition having higher IQs on average than participants in the negative mood condition—then it is unclear whether it was the positive moods or the higher IQs that caused participants in the first condition to score higher. One way to avoid confounding variables is by holding extraneous variables constant. For example, one could prevent IQ from becoming a confounding variable by limiting participants only to those with IQs of exactly 100. But this approach is not always desirable for reasons we have already discussed. A second and much more general approach—random assignment to conditions—will be discussed in detail shortly.

Figure 6.1 Hypothetical Results From a Study on the Effect of Mood on Memory

Because IQ also differs across conditions, it is a confounding variable.

Key Takeaways

• An experiment is a type of empirical study that features the manipulation of an independent variable, the measurement of a dependent variable, and control of extraneous variables.
• Studies are high in internal validity to the extent that the way they are conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Experiments are generally high in internal validity because of the manipulation of the independent variable and control of extraneous variables.
• Studies are high in external validity to the extent that the result can be generalized to people and situations beyond those actually studied. Although experiments can seem “artificial”—and low in external validity—it is important to consider whether the psychological processes under study are likely to operate in other people and situations.
• Practice: List five variables that can be manipulated by the researcher in an experiment. List five variables that cannot be manipulated by the researcher in an experiment.

Practice: For each of the following topics, decide whether that topic could be studied using an experimental research design and explain why or why not.

• Effect of parietal lobe damage on people’s ability to do basic arithmetic.
• Effect of being clinically depressed on the number of close friendships people have.
• Effect of group training on the social skills of teenagers with Asperger’s syndrome.
• Effect of paying people to take an IQ test on their performance on that test.

Cialdini, R. (2005, April). Don’t throw in the towel: Use social influence research. APS Observer . Retrieved from http://www.psychologicalscience.org/observer/getArticle.cfm?id=1762 .

Fredrickson, B. L., Roberts, T.-A., Noll, S. M., Quinn, D. M., & Twenge, J. M. (1998). The swimsuit becomes you: Sex differences in self-objectification, restrained eating, and math performance. Journal of Personality and Social Psychology, 75 , 269–284.

Stanovich, K. E. (2010). How to think straight about psychology (9th ed.). Boston, MA: Allyn & Bacon.

Research Methods in Psychology Copyright © 2016 by University of Minnesota is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Chapter 6: Experimental Research

Experiment Basics

Learning Objectives

• Explain what an experiment is and recognize examples of studies that are experiments and studies that are not experiments.
• Explain what internal validity is and why experiments are considered to be high in internal validity.
• Explain what external validity is and evaluate studies in terms of their external validity.
• Distinguish between the manipulation of the independent variable and control of extraneous variables and explain the importance of each.
• Recognize examples of confounding variables and explain how they affect the internal validity of a study.

What Is an Experiment?

As we saw earlier in the book, an  experiment  is a type of study designed specifically to answer the question of whether there is a causal relationship between two variables. In other words, whether changes in an independent variable  cause  changes in a dependent variable. Experiments have two fundamental features. The first is that the researchers manipulate, or systematically vary, the level of the independent variable. The different levels of the independent variable are called conditions . For example, in Darley and Latané’s experiment, the independent variable was the number of witnesses that participants believed to be present. The researchers manipulated this independent variable by telling participants that there were either one, two, or five other students involved in the discussion, thereby creating three conditions. For a new researcher, it is easy to confuse  these terms by believing there are three independent variables in this situation: one, two, or five students involved in the discussion, but there is actually only one independent variable (number of witnesses) with three different conditions (one, two or five students). The second fundamental feature of an experiment is that the researcher controls, or minimizes the variability in, variables other than the independent and dependent variable. These other variables are called extraneous variables . Darley and Latané tested all their participants in the same room, exposed them to the same emergency situation, and so on. They also randomly assigned their participants to conditions so that the three groups would be similar to each other to begin with. Notice that although the words  manipulation  and  control  have similar meanings in everyday language, researchers make a clear distinction between them. They manipulate  the independent variable by systematically changing its levels and control  other variables by holding them constant.

Four Big Validities

When we read about psychology experiments with a critical view, one question to ask is “is this study valid?” However, that question is not as straightforward as it seems because in psychology, there are many different kinds of validities. Researchers have focused on four validities to help assess whether an experiment is sound (Judd & Kenny, 1981; Morling, 2014) [1] [2] :internal validity, external validity, construct validity, and statistical validity. We will explore each validity in depth.

Internal Validity

Recall that two variables being statistically related does not necessarily mean that one causes the other. “Correlation does not imply causation.” For example, if it were the case that people who exercise regularly are happier than people who do not exercise regularly, this implication would not necessarily mean that exercising increases people’s happiness. It could mean instead that greater happiness causes people to exercise (the directionality problem) or that something like better physical health causes people to exercise   and  be happier (the third-variable problem).

The purpose of an experiment, however, is to show that two variables are statistically related and to do so in a way that supports the conclusion that the independent variable caused any observed differences in the dependent variable. The logic is based on this assumption : If the researcher creates two or more highly similar conditions and then manipulates the independent variable to produce just  one  difference between them, then any later difference between the conditions must have been caused by the independent variable. For example, because the only difference between Darley and Latané’s conditions was the number of students that participants believed to be involved in the discussion, this difference in belief must have been responsible for differences in helping between the conditions.

An empirical study is said to be high in  internal validity  if the way it was conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Thus experiments are high in internal validity because the way they are conducted—with the manipulation of the independent variable and the control of extraneous variables—provides strong support for causal conclusions.

External Validity

At the same time, the way that experiments are conducted sometimes leads to a different kind of criticism. Specifically, the need to manipulate the independent variable and control extraneous variables means that experiments are often conducted under conditions that seem artificial (Bauman, McGraw, Bartels, & Warren, 2014) [3] .In many psychology experiments, the participants are all undergraduate students and come to a classroom or laboratory to fill out a series of paper-and-pencil questionnaires or to perform a carefully designed computerized task. Consider, for example, an experiment in which researcher Barbara Fredrickson and her colleagues had undergraduate students come to a laboratory on campus and complete a math test while wearing a swimsuit (Fredrickson, Roberts, Noll, Quinn, & Twenge, 1998) [4] .At first, this manipulation might seem silly. When will undergraduate students ever have to complete math tests in their swimsuits outside of this experiment?

The issue we are confronting is that of external validity . An empirical study is high in external validity if the way it was conducted supports generalizing the results to people and situations beyond those actually studied. As a general rule, studies are higher in external validity when the participants and the situation studied are similar to those that the researchers want to generalize to and participants encounter everyday, often described as mundane realism . Imagine, for example, that a group of researchers is interested in how shoppers in large grocery stores are affected by whether breakfast cereal is packaged in yellow or purple boxes. Their study would be high in external validity and have high mundane realism if they studied the decisions of ordinary people doing their weekly shopping in a real grocery store. If the shoppers bought much more cereal in purple boxes, the researchers would be fairly confident that this increase would be true for other shoppers in other stores. Their study would be relatively low in external validity, however, if they studied a sample of undergraduate students in a laboratory at a selective university who merely judged the appeal of various colours presented on a computer screen; however, this study would have high psychological realism where the same mental process is used in both the laboratory and in the real world.  If the students judged purple to be more appealing than yellow, the researchers would not be very confident that this preference is relevant to grocery shoppers’ cereal-buying decisions because of low external validity but they could be confident that the visual processing of colours has high psychological realism.

We should be careful, however, not to draw the blanket conclusion that experiments are low in external validity. One reason is that experiments need not seem artificial. Consider that Darley and Latané’s experiment provided a reasonably good simulation of a real emergency situation. Or consider  field experiments  that are conducted entirely outside the laboratory. In one such experiment, Robert Cialdini and his colleagues studied whether hotel guests choose to reuse their towels for a second day as opposed to having them washed as a way of conserving water and energy (Cialdini, 2005) [5] . These researchers manipulated the message on a card left in a large sample of hotel rooms. One version of the message emphasized showing respect for the environment, another emphasized that the hotel would donate a portion of their savings to an environmental cause, and a third emphasized that most hotel guests choose to reuse their towels. The result was that guests who received the message that most hotel guests choose to reuse their towels reused their own towels substantially more often than guests receiving either of the other two messages. Given the way they conducted their study, it seems very likely that their result would hold true for other guests in other hotels.

A second reason not to draw the blanket conclusion that experiments are low in external validity is that they are often conducted to learn about psychological processes  that are likely to operate in a variety of people and situations. Let us return to the experiment by Fredrickson and colleagues. They found that the women in their study, but not the men, performed worse on the math test when they were wearing swimsuits. They argued that this gender difference was due to women’s greater tendency to objectify themselves—to think about themselves from the perspective of an outside observer—which diverts their attention away from other tasks. They argued, furthermore, that this process of self-objectification and its effect on attention is likely to operate in a variety of women and situations—even if none of them ever finds herself taking a math test in her swimsuit.

Construct Validity

In addition to the generalizability of the results of an experiment, another element to scrutinize in a study is the quality of the experiment’s manipulations, or the construct validity . The research question that Darley and Latané started with is “does helping behaviour become diffused?” They hypothesized that participants in a lab would be less likely to help when they believed there were more potential helpers besides themselves. This conversion from research question to experiment design is called operationalization (see Chapter 2 for more information about the operational definition). Darley and Latané operationalized the independent variable of diffusion of responsibility by increasing the number of potential helpers. In evaluating this design, we would say that the construct validity was very high because the experiment’s manipulations very clearly speak to the research question; there was a crisis, a way for the participant to help, and increasing the number of other students involved in the discussion, they provided a way to test diffusion.

What if the number of conditions in Darley and Latané’s study changed? Consider if there were only two conditions: one student involved in the discussion or two. Even though we may see a decrease in helping by adding another person, it may not be a clear demonstration of diffusion of responsibility, just merely the presence of others. We might think it was a form of Bandura’s social inhibition  (discussed in Chapter 4). The construct validity would be lower. However, had there been five conditions, perhaps we would see the decrease continue with more people in the discussion or perhaps it would plateau after a certain number of people. In that situation, we may not necessarily be learning more about diffusion of responsibility or it may become a different phenomenon. By adding more conditions, the construct validity may not get higher. When designing your own experiment, consider how well the research question is operationalized your study.

Statistical Validity

A common critique of experiments is that a study did not have enough participants. The main reason for this criticism is that it is difficult to generalize about a population from a small sample. At the outset, it seems as though this critique is about external validity but there are studies where small sample sizes are not a problem (Chapter 10 will discuss how small samples, even of only 1 person, are still very illuminating for psychology research). Therefore, small sample sizes are actually a critique of statistical validity . The statistical validity speaks to whether the statistics conducted in the study support the conclusions that are made.

Proper statistical analysis should be conducted on the data to determine whether the difference or relationship that was predicted was found. The number of conditions and the number of total participants will determine the overall size of the effect. With this information, a power analysis can be conducted to ascertain whether you are likely to find a real difference. When designing a study, it is best to think about the power analysis so that the appropriate number of participants can be recruited and tested (more on effect sizes in Chapter 12). To design a statistically valid experiment, thinking about the statistical tests at the beginning of the design will help ensure the results can be believed.

Prioritizing Validities

These four big validities–internal, external, construct, and statistical–are useful to keep in mind when both reading about other experiments and designing your own. However, researchers must prioritize and often it is not possible to have high validity in all four areas. In Cialdini’s study on towel usage in hotels, the external validity was high but the statistical validity was more modest. This discrepancy does not invalidate the study but it shows where there may be room for improvement for future follow-up studies (Goldstein, Cialdini, & Griskevicius, 2008) [6] . Morling (2014) points out that most psychology studies have high internal and construct validity but sometimes sacrifice external validity.

Manipulation of the Independent Variable

Again, to  manipulate  an independent variable means to change its level systematically so that different groups of participants are exposed to different levels of that variable, or the same group of participants is exposed to different levels at different times. For example, to see whether expressive writing affects people’s health, a researcher might instruct some participants to write about traumatic experiences and others to write about neutral experiences. As discussed earlier in this chapter, the different levels of the independent variable are referred to as  conditions , and researchers often give the conditions short descriptive names to make it easy to talk and write about them. In this case, the conditions might be called the “traumatic condition” and the “neutral condition.”

Notice that the manipulation of an independent variable must involve the active intervention of the researcher. Comparing groups of people who differ on the independent variable before the study begins is not the same as manipulating that variable. For example, a researcher who compares the health of people who already keep a journal with the health of people who do not keep a journal has not manipulated this variable and therefore not conducted an experiment. This distinction  is important because groups that already differ in one way at the beginning of a study are likely to differ in other ways too. For example, people who choose to keep journals might also be more conscientious, more introverted, or less stressed than people who do not. Therefore, any observed difference between the two groups in terms of their health might have been caused by whether or not they keep a journal, or it might have been caused by any of the other differences between people who do and do not keep journals. Thus the active manipulation of the independent variable is crucial for eliminating the third-variable problem.

Of course, there are many situations in which the independent variable cannot be manipulated for practical or ethical reasons and therefore an experiment is not possible. For example, whether or not people have a significant early illness experience cannot be manipulated, making it impossible to conduct an experiment on the effect of early illness experiences on the development of hypochondriasis. This caveat does not mean it is impossible to study the relationship between early illness experiences and hypochondriasis—only that it must be done using nonexperimental approaches. We will discuss this type of methodology in detail later in the book.

In many experiments, the independent variable is a construct that can only be manipulated indirectly. For example, a researcher might try to manipulate participants’ stress levels indirectly by telling some of them that they have five minutes to prepare a short speech that they will then have to give to an audience of other participants. In such situations, researchers often include a manipulation check  in their procedure. A manipulation check is a separate measure of the construct the researcher is trying to manipulate. For example, researchers trying to manipulate participants’ stress levels might give them a paper-and-pencil stress questionnaire or take their blood pressure—perhaps right after the manipulation or at the end of the procedure—to verify that they successfully manipulated this variable.

Control of Extraneous Variables

As we have seen previously in the chapter, an  extraneous variable  is anything that varies in the context of a study other than the independent and dependent variables. In an experiment on the effect of expressive writing on health, for example, extraneous variables would include participant variables (individual differences) such as their writing ability, their diet, and their shoe size. They would also include situational or task variables such as the time of day when participants write, whether they write by hand or on a computer, and the weather. Extraneous variables pose a problem because many of them are likely to have some effect on the dependent variable. For example, participants’ health will be affected by many things other than whether or not they engage in expressive writing. This influencing factor can make it difficult to separate the effect of the independent variable from the effects of the extraneous variables, which is why it is important to  control  extraneous variables by holding them constant.

Extraneous Variables as “Noise”

Extraneous variables make it difficult to detect the effect of the independent variable in two ways. One is by adding variability or “noise” to the data. Imagine a simple experiment on the effect of mood (happy vs. sad) on the number of happy childhood events people are able to recall. Participants are put into a negative or positive mood (by showing them a happy or sad video clip) and then asked to recall as many happy childhood events as they can. Table 6.1 shows what the data might look like if there were no extraneous variables and the number of happy childhood events participants recalled was affected only by their moods. Every participant in the happy mood condition recalled exactly four happy childhood events, and every participant in the sad mood condition recalled exactly three. The effect of mood here is quite obvious.

In reality, however, the data would probably look more like those Table 6.2 . Even in the happy mood condition, some participants would recall fewer happy memories because they have fewer to draw on, use less effective recall strategies, or are less motivated. And even in the sad mood condition, some participants would recall more happy childhood memories because they have more happy memories to draw on, they use more effective recall strategies, or they are more motivated.

Although the mean difference between the two groups is the same as in the idealized data, this difference is much less obvious in the context of the greater variability in the data. Thus one reason researchers try to control extraneous variables is so their data look more like the idealized data in  Table 6.1 , which makes the effect of the independent variable easier to detect (although real data never look quite  that  good).

One way to control extraneous variables is to hold them constant. This technique can mean holding situation or task variables constant by testing all participants in the same location, giving them identical instructions, treating them in the same way, and so on. It can also mean holding participant variables constant. For example, many studies of language limit participants to right-handed people, who generally have their language areas isolated in their left cerebral hemispheres. Left-handed people are more likely to have their language areas isolated in their right cerebral hemispheres or distributed across both hemispheres, which can change the way they process language and thereby add noise to the data.

In principle, researchers can control extraneous variables by limiting participants to one very specific category of person, such as 20-year-old, heterosexual, female, right-handed psychology majors. The obvious downside to this approach is that it would lower the external validity of the study—in particular, the extent to which the results can be generalized beyond the people actually studied. For example, it might be unclear whether results obtained with a sample of younger heterosexual women would apply to older homosexual men. In many situations, the advantages of a diverse sample outweigh the reduction in noise achieved by a homogeneous one.

Extraneous Variables as Confounding Variables

The second way that extraneous variables can make it difficult to detect the effect of the independent variable is by becoming confounding variables. A confounding variable  is an extraneous variable that differs on average across  levels of the independent variable. For example, in almost all experiments, participants’ intelligence quotients (IQs) will be an extraneous variable. But as long as there are participants with lower and higher IQs at each level of the independent variable so that the average IQ is roughly equal, then this variation is probably acceptable (and may even be desirable). What would be bad, however, would be for participants at one level of the independent variable to have substantially lower IQs on average and participants at another level to have substantially higher IQs on average. In this case, IQ would be a confounding variable.

To confound means to confuse , and this effect is exactly why confounding variables are undesirable. Because they differ across conditions—just like the independent variable—they provide an alternative explanation for any observed difference in the dependent variable.  Figure 6.1  shows the results of a hypothetical study, in which participants in a positive mood condition scored higher on a memory task than participants in a negative mood condition. But if IQ is a confounding variable—with participants in the positive mood condition having higher IQs on average than participants in the negative mood condition—then it is unclear whether it was the positive moods or the higher IQs that caused participants in the first condition to score higher. One way to avoid confounding variables is by holding extraneous variables constant. For example, one could prevent IQ from becoming a confounding variable by limiting participants only to those with IQs of exactly 100. But this approach is not always desirable for reasons we have already discussed. A second and much more general approach—random assignment to conditions—will be discussed in detail shortly.

Key Takeaways

• An experiment is a type of empirical study that features the manipulation of an independent variable, the measurement of a dependent variable, and control of extraneous variables.
• Studies are high in internal validity to the extent that the way they are conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Experiments are generally high in internal validity because of the manipulation of the independent variable and control of extraneous variables.
• Studies are high in external validity to the extent that the result can be generalized to people and situations beyond those actually studied. Although experiments can seem “artificial”—and low in external validity—it is important to consider whether the psychological processes under study are likely to operate in other people and situations.
• Practice: List five variables that can be manipulated by the researcher in an experiment. List five variables that cannot be manipulated by the researcher in an experiment.
• Effect of parietal lobe damage on people’s ability to do basic arithmetic.
• Effect of being clinically depressed on the number of close friendships people have.
• Effect of group training on the social skills of teenagers with Asperger’s syndrome.
• Effect of paying people to take an IQ test on their performance on that test.
• Judd, C.M. & Kenny, D.A. (1981). Estimating the effects of social interventions . Cambridge, MA: Cambridge University Press. ↵
• Morling, B. (2014, April). Teach your students to be better consumers. APS Observer . Retrieved from http://www.psychologicalscience.org/index.php/publications/observer/2014/april-14/teach-your-students-to-be-better-consumers.html ↵
• Bauman, C.W., McGraw, A.P., Bartels, D.M., & Warren, C. (2014). Revisiting external validity: Concerns about trolley problems and other sacrificial dilemmas in moral psychology. Social and Personality Psychology Compass, 8/9 , 536-554. ↵
• Fredrickson, B. L., Roberts, T.-A., Noll, S. M., Quinn, D. M., & Twenge, J. M. (1998). The swimsuit becomes you: Sex differences in self-objectification, restrained eating, and math performance. Journal of Personality and Social Psychology, 75 , 269–284. ↵
• Cialdini, R. (2005, April). Don’t throw in the towel: Use social influence research. APS Observer . Retrieved from http://www.psychologicalscience.org/index.php/publications/observer/2005/april-05/dont-throw-in-the-towel-use-social-influence-research.html ↵
• Goldstein, N. J., Cialdini, R. B., & Griskevicius, V. (2008). A room with a viewpoint: Using social norms to motivate environmental conservation in hotels. Journal of Consumer Research, 35 , 472–482. ↵

A study in which the researcher manipulates the independent variable.

The different levels of the independent variable.

Anything that varies in the context of a study other than the independent and dependent variables.

When the way an experiment was conducted supports the conclusion that the independent variable caused observed differences in the dependent variable. These studies provide strong support for causal conclusions.

When the way a study is conducted supports generalizing the results to people and situations beyond those actually studied.

The participants and the situation studied are similar to those that the researchers want to generalize to and participants encounter everyday.

The same mental process is used in both the laboratory and in the real world.

The quality of the experiment’s manipulations.

Conversion from research question to experiment design.

Whether the statistics conducted in the study support the conclusions that are made.

To change an independent variable’s level systematically so that different groups of participants are exposed to different levels of that variable, or the same group of participants is exposed to different levels at different times.

A separate measure of the construct the researcher is trying to manipulate.

Method of holding extraneous variables at a constant.

An extraneous variable that differs on average across levels of the independent variable.

Research Methods in Psychology - 2nd Canadian Edition Copyright © 2015 by Paul C. Price, Rajiv Jhangiani, & I-Chant A. Chiang is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Experimental Research

In the late 1960s social psychologists John Darley and Bibb Latané proposed a counter-intuitive hypothesis. The more witnesses there are to an accident or a crime, the less likely any of them is to help the victim (Darley & Latané, 1968) [1] .

They also suggested the theory that this phenomenon occurs because each witness feels less responsible for helping—a process referred to as the “diffusion of responsibility.” Darley and Latané noted that their ideas were consistent with many real-world cases. For example, a New York woman named Catherine “Kitty” Genovese was assaulted and murdered while several witnesses evidently failed to help. But Darley and Latané also understood that such isolated cases did not provide convincing evidence for their hypothesized “bystander effect.” There was no way to know, for example, whether any of the witnesses to Kitty Genovese’s murder would have helped had there been fewer of them.

So to test their hypothesis, Darley and Latané created a simulated emergency situation in a laboratory. Each of their university student participants was isolated in a small room and told that they would be having a discussion about university life with other students via an intercom system. Early in the discussion, however, one of the students began having what seemed to be an epileptic seizure. Over the intercom came the following: “I could really-er-use some help so if somebody would-er-give me a little h-help-uh-er-er-er-er-er c-could somebody-er-er-help-er-uh-uh-uh (choking sounds)…I’m gonna die-er-er-I’m…gonna die-er-help-er-er-seizure-er- [chokes, then quiet]” (Darley & Latané, 1968, p. 379) .

In actuality, there were no other students. These comments had been prerecorded and were played back to create the appearance of a real emergency. The key to the study was that some participants were told that the discussion involved only one other student (the victim), others were told that it involved two other students, and still others were told that it included five other students. Because this was the only difference between these three groups of participants, any difference in their tendency to help the victim would have to have been caused by it. And sure enough, the likelihood that the participant left the room to seek help for the “victim” decreased from 85% to 62% to 31% as the number of “witnesses” increased.

The Parable of the 38 Witnesses

The story of Kitty Genovese has been told and retold in numerous psychology textbooks. The standard version is that there were 38 witnesses to the crime, that all of them watched (or listened) for an extended period of time, and that none of them did anything to help. However, recent scholarship suggests that the standard story is inaccurate in many ways (Manning, Levine, & Collins, 2007) [2] . For example, only six eyewitnesses testified at the trial, none of them was aware that they were witnessing a lethal assault, and there have been several reports of witnesses calling the police or even coming to the aid of Kitty Genovese. Although the standard story inspired a long line of research on the bystander effect and the diffusion of responsibility, it may also have directed researchers’ and students’ attention away from other equally interesting and important issues in the psychology of helping—including the conditions in which people do in fact respond collectively to emergency situations.

The research that Darley and Latané conducted was a particular kind of study called an experiment. Experiments are used to determine not only whether there is a meaningful relationship between two variables but also whether the relationship is a causal one that is supported by statistical analysis. For this reason, experiments are one of the most common and useful tools in the psychological researcher’s toolbox. In this chapter, we look at experiments in detail. We will first consider what sets experiments apart from other kinds of studies and why they support causal conclusions while other kinds of studies do not. We then look at two basic ways of designing an experiment—between-subjects designs and within-subjects designs—and discuss their pros and cons. Finally, we consider several important practical issues that arise when conducting experiments.

• Darley, J. M., & Latané, B. (1968). Bystander intervention in emergencies: Diffusion of responsibility. Journal of Personality and Social Psychology, 4 , 377–383. ↵
• Manning, R., Levine, M., & Collins, A. (2007). The Kitty Genovese murder and the social psychology of helping: The parable of the 38 witnesses. American Psychologist, 62 , 555–562. ↵

Research Methods in Psychology Copyright © 2019 by Rajiv S. Jhangiani, I-Chant A. Chiang, Carrie Cuttler, & Dana C. Leighton is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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7 Famous Psychology Experiments

Many famous experiments studying human behavior have impacted our fundamental understanding of psychology. Though some could not be repeated today due to breaches in ethical boundaries, that does not diminish the significance of those psychological studies. Some of these important findings include a greater awareness of depression and its symptoms, how people learn behaviors through the process of association and how individuals conform to a group.

Below, we take a look at seven famous psychological experiments that greatly influenced the field of psychology and our understanding of human behavior.

The Little Albert Experiment, 1920

A John’s Hopkins University professor, Dr. John B. Watson, and a graduate student wanted to test a learning process called classical conditioning. Classical conditioning involves learning involuntary or automatic behaviors by association, and Dr. Watson thought it formed the bedrock of human psychology.

A nine-month-old toddler, dubbed “Albert B,” was volunteered for Dr. Watson and Rosalie Rayner ‘s experiment. Albert played with white furry objects, and at first, the toddler displayed joy and affection. Over time, as he played with the objects, Dr. Watson would make a loud noise behind the child’s head to frighten him. After numerous trials, Albert was conditioned to be afraid when he saw white furry objects.

The study proved that humans could be conditioned to enjoy or fear something, which many psychologists believe could explain why people have irrational fears and how they may have developed early in life. This is a great example of experimental study psychology.

Stanford Prison Experiment, 1971

Stanford professor Philip Zimbardo wanted to learn how individuals conformed to societal roles. He wondered, for example, whether the tense relationship between prison guards and inmates in jails had more to do with the personalities of each or the environment.

During Zimbardo’s experiment , 24 male college students were assigned to be either a prisoner or a guard. The prisoners were held in a makeshift prison inside the basement of Stanford’s psychology department. They went through a standard booking process designed to take away their individuality and make them feel anonymous. Guards were given eight-hour shifts and tasked to treat the prisoners just like they would in real life.

Zimbardo found rather quickly that both the guards and prisoners fully adapted to their roles; in fact, he had to shut down the experiment after six days because it became too dangerous. Zimbardo even admitted he began thinking of himself as a police superintendent rather than a psychologist. The study confirmed that people will conform to the social roles they’re expected to play, especially overly stereotyped ones such as prison guards.

“We realized how ordinary people could be readily transformed from the good Dr. Jekyll to the evil Mr. Hyde,” Zimbardo wrote.

The Asch Conformity Study, 1951

Solomon Asch, a Polish-American social psychologist, was determined to see whether an individual would conform to a group’s decision, even if the individual knew it was incorrect. Conformity is defined by the American Psychological Association as the adjustment of a person’s opinions or thoughts so that they fall closer in line with those of other people or the normative standards of a social group or situation.

In his experiment , Asch selected 50 male college students to participate in a “vision test.” Individuals would have to determine which line on a card was longer. However, the individuals at the center of the experiment did not know that the other people taking the test were actors following scripts, and at times selected the wrong answer on purpose. Asch found that, on average over 12 trials, nearly one-third of the naive participants conformed with the incorrect majority, and only 25 percent never conformed to the incorrect majority. In the control group that featured only the participants and no actors, less than one percent of participants ever chose the wrong answer.

Asch’s experiment showed that people will conform to groups to fit in (normative influence) because of the belief that the group was better informed than the individual. This explains why some people change behaviors or beliefs when in a new group or social setting, even when it goes against past behaviors or beliefs.

The Bobo Doll Experiment, 1961, 1963

Stanford University professor Albert Bandura wanted to put the social learning theory into action. Social learning theory suggests that people can acquire new behaviors “through direct experience or by observing the behavior of others.” Using a Bobo doll , which is a blow-up toy in the shape of a life-size bowling pin, Bandura and his team tested whether children witnessing acts of aggression would copy them.

Bandura and two colleagues selected 36 boys and 36 girls between the ages of 3 and 6 from the Stanford University nursery and split them into three groups of 24. One group watched adults behaving aggressively toward the Bobo doll. In some cases, the adult subjects hit the doll with a hammer or threw it in the air. Another group was shown an adult playing with the Bobo doll in a non-aggressive manner, and the last group was not shown a model at all, just the Bobo doll.

After each session, children were taken to a room with toys and studied to see how their play patterns changed. In a room with aggressive toys (a mallet, dart guns, and a Bobo doll) and non-aggressive toys (a tea set, crayons, and plastic farm animals), Bandura and his colleagues observed that children who watched the aggressive adults were more likely to imitate the aggressive responses.

Unexpectedly, Bandura found that female children acted more physically aggressive after watching a male subject and more verbally aggressive after watching a female subject. The results of the study highlight how children learn behaviors from observing others.

The Learned Helplessness Experiment, 1965

Martin Seligman wanted to research a different angle related to Dr. Watson’s study of classical conditioning. In studying conditioning with dogs, Seligman made an astute observation : the subjects, which had already been conditioned to expect a light electric shock if they heard a bell, would sometimes give up after another negative outcome, rather than searching for the positive outcome.

Under normal circumstances, animals will always try to get away from negative outcomes. When Seligman tested his experiment on animals who hadn’t been previously conditioned, the animals attempted to find a positive outcome. Oppositely, the dogs who had been already conditioned to expect a negative response assumed there would be another negative response waiting for them, even in a different situation.

The conditioned dogs’ behavior became known as learned helplessness, the idea that some subjects won’t try to get out of a negative situation because past experiences have forced them to believe they are helpless. The study’s findings shed light on depression and its symptoms in humans.

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The Milgram Experiment, 1963

In the wake of the horrific atrocities carried out by Nazi Germany during World War II, Stanley Milgram wanted to test the levels of obedience to authority. The Yale University professor wanted to study if people would obey commands, even when it conflicted with the person’s conscience.

Participants of the condensed study , 40 males between the ages of 20 and 50, were split into learners and teachers. Though it seemed random, actors were always chosen as the learners, and unsuspecting participants were always the teachers. A learner was strapped to a chair with electrodes in one room while the experimenter äóñ another actor äóñ and a teacher went into another.

The teacher and learner went over a list of word pairs that the learner was told to memorize. When the learner incorrectly paired a set of words together, the teacher would shock the learner. The teacher believed the shocks ranged from mild all the way to life-threatening. In reality, the learner, who intentionally made mistakes, was not being shocked.

As the voltage of the shocks increased and the teachers became aware of the believed pain caused by them, some refused to continue the experiment. After prodding by the experimenter, 65 percent resumed. From the study, Milgram devised the agency theory , which suggests that people allow others to direct their actions because they believe the authority figure is qualified and will accept responsibility for the outcomes. Milgram’s findings help explain how people can make decisions against their own conscience, such as when participating in a war or genocide.

The Halo Effect Experiment, 1977

University of Michigan professors Richard Nisbett and Timothy Wilson were interested in following up a study from 50 years earlier on a concept known as the halo effect . In the 1920s, American psychologist Edward Thorndike researched a phenomenon in the U.S. military that showed cognitive bias. This is an error in how we think that affects how we perceive people and make judgements and decisions based on those perceptions.

In 1977, Nisbett and Wilson tested the halo effect using 118 college students (62 males, 56 females). Students were divided into two groups and were asked to evaluate a male Belgian teacher who spoke English with a heavy accent. Participants were shown one of two videotaped interviews with the teacher on a television monitor. The first interview showed the teacher interacting cordially with students, and the second interview showed the teacher behaving inhospitably. The subjects were then asked to rate the teacher’s physical appearance, mannerisms, and accent on an eight-point scale from appealing to irritating.

Nisbett and Wilson found that on physical appearance alone, 70 percent of the subjects rated the teacher as appealing when he was being respectful and irritating when he was cold. When the teacher was rude, 80 percent of the subjects rated his accent as irritating, as compared to nearly 50 percent when he was being kind.

The updated study on the halo effect shows that cognitive bias isn’t exclusive to a military environment. Cognitive bias can get in the way of making the correct decision, whether it’s during a job interview or deciding whether to buy a product that’s been endorsed by a celebrity we admire.

How Experiments Have Impacted Psychology Today

Contemporary psychologists have built on the findings of these studies to better understand human behaviors, mental illnesses, and the link between the mind and body. For their contributions to psychology, Watson, Bandura, Nisbett and Zimbardo were all awarded Gold Medals for Life Achievement from the American Psychological Foundation. Become part of the next generation of influential psychologists with King University’s online bachelor’s in psychology . Take advantage of King University’s flexible online schedule and complete the major coursework of your degree in as little as 16 months. Plus, as a psychology major, King University will prepare you for graduate school with original research on student projects as you pursue your goal of being a psychologist.

• The 25 Most Influential Psychological Experiments in History

While each year thousands and thousands of studies are completed in the many specialty areas of psychology, there are a handful that, over the years, have had a lasting impact in the psychological community as a whole. Some of these were dutifully conducted, keeping within the confines of ethical and practical guidelines. Others pushed the boundaries of human behavior during their psychological experiments and created controversies that still linger to this day. And still others were not designed to be true psychological experiments, but ended up as beacons to the psychological community in proving or disproving theories.

This is a list of the 25 most influential psychological experiments still being taught to psychology students of today.

1. A Class Divided

Study conducted by: jane elliott.

Study Conducted in 1968 in an Iowa classroom

Experiment Details: Jane Elliott’s famous experiment was inspired by the assassination of Dr. Martin Luther King Jr. and the inspirational life that he led. The third grade teacher developed an exercise, or better yet, a psychological experiment, to help her Caucasian students understand the effects of racism and prejudice.

Elliott divided her class into two separate groups: blue-eyed students and brown-eyed students. On the first day, she labeled the blue-eyed group as the superior group and from that point forward they had extra privileges, leaving the brown-eyed children to represent the minority group. She discouraged the groups from interacting and singled out individual students to stress the negative characteristics of the children in the minority group. What this exercise showed was that the children’s behavior changed almost instantaneously. The group of blue-eyed students performed better academically and even began bullying their brown-eyed classmates. The brown-eyed group experienced lower self-confidence and worse academic performance. The next day, she reversed the roles of the two groups and the blue-eyed students became the minority group.

At the end of the experiment, the children were so relieved that they were reported to have embraced one another and agreed that people should not be judged based on outward appearances. This exercise has since been repeated many times with similar outcomes.

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2. Asch Conformity Study

Study conducted by: dr. solomon asch.

Study Conducted in 1951 at Swarthmore College

Experiment Details: Dr. Solomon Asch conducted a groundbreaking study that was designed to evaluate a person’s likelihood to conform to a standard when there is pressure to do so.

A group of participants were shown pictures with lines of various lengths and were then asked a simple question: Which line is longest? The tricky part of this study was that in each group only one person was a true participant. The others were actors with a script. Most of the actors were instructed to give the wrong answer. Strangely, the one true participant almost always agreed with the majority, even though they knew they were giving the wrong answer.

The results of this study are important when we study social interactions among individuals in groups. This study is a famous example of the temptation many of us experience to conform to a standard during group situations and it showed that people often care more about being the same as others than they do about being right. It is still recognized as one of the most influential psychological experiments for understanding human behavior.

3. Bobo Doll Experiment

Study conducted by: dr. alburt bandura.

Study Conducted between 1961-1963 at Stanford University

In his groundbreaking study he separated participants into three groups:

• one was exposed to a video of an adult showing aggressive behavior towards a Bobo doll
• another was exposed to video of a passive adult playing with the Bobo doll
• the third formed a control group

Children watched their assigned video and then were sent to a room with the same doll they had seen in the video (with the exception of those in the control group). What the researcher found was that children exposed to the aggressive model were more likely to exhibit aggressive behavior towards the doll themselves. The other groups showed little imitative aggressive behavior. For those children exposed to the aggressive model, the number of derivative physical aggressions shown by the boys was 38.2 and 12.7 for the girls.

The study also showed that boys exhibited more aggression when exposed to aggressive male models than boys exposed to aggressive female models. When exposed to aggressive male models, the number of aggressive instances exhibited by boys averaged 104. This is compared to 48.4 aggressive instances exhibited by boys who were exposed to aggressive female models.

While the results for the girls show similar findings, the results were less drastic. When exposed to aggressive female models, the number of aggressive instances exhibited by girls averaged 57.7. This is compared to 36.3 aggressive instances exhibited by girls who were exposed to aggressive male models. The results concerning gender differences strongly supported Bandura’s secondary prediction that children will be more strongly influenced by same-sex models. The Bobo Doll Experiment showed a groundbreaking way to study human behavior and it’s influences.

4. Car Crash Experiment

Study conducted by: elizabeth loftus and john palmer.

Study Conducted in 1974 at The University of California in Irvine

The participants watched slides of a car accident and were asked to describe what had happened as if they were eyewitnesses to the scene. The participants were put into two groups and each group was questioned using different wording such as “how fast was the car driving at the time of impact?” versus “how fast was the car going when it smashed into the other car?” The experimenters found that the use of different verbs affected the participants’ memories of the accident, showing that memory can be easily distorted.

This research suggests that memory can be easily manipulated by questioning technique. This means that information gathered after the event can merge with original memory causing incorrect recall or reconstructive memory. The addition of false details to a memory of an event is now referred to as confabulation. This concept has very important implications for the questions used in police interviews of eyewitnesses.

5. Cognitive Dissonance Experiment

Study conducted by: leon festinger and james carlsmith.

Study Conducted in 1957 at Stanford University

Experiment Details: The concept of cognitive dissonance refers to a situation involving conflicting:

This conflict produces an inherent feeling of discomfort leading to a change in one of the attitudes, beliefs or behaviors to minimize or eliminate the discomfort and restore balance.

Cognitive dissonance was first investigated by Leon Festinger, after an observational study of a cult that believed that the earth was going to be destroyed by a flood. Out of this study was born an intriguing experiment conducted by Festinger and Carlsmith where participants were asked to perform a series of dull tasks (such as turning pegs in a peg board for an hour). Participant’s initial attitudes toward this task were highly negative.

They were then paid either $1 or $20 to tell a participant waiting in the lobby that the tasks were really interesting. Almost all of the participants agreed to walk into the waiting room and persuade the next participant that the boring experiment would be fun. When the participants were later asked to evaluate the experiment, the participants who were paid only $1 rated the tedious task as more fun and enjoyable than the participants who were paid $20 to lie.

Being paid only $1 is not sufficient incentive for lying and so those who were paid $1 experienced dissonance. They could only overcome that cognitive dissonance by coming to believe that the tasks really were interesting and enjoyable. Being paid $20 provides a reason for turning pegs and there is therefore no dissonance.

6. Fantz’s Looking Chamber

Study conducted by: robert l. fantz.

Study Conducted in 1961 at the University of Illinois

Experiment Details: The study conducted by Robert L. Fantz is among the simplest, yet most important in the field of infant development and vision. In 1961, when this experiment was conducted, there very few ways to study what was going on in the mind of an infant. Fantz realized that the best way was to simply watch the actions and reactions of infants. He understood the fundamental factor that if there is something of interest near humans, they generally look at it.

To test this concept, Fantz set up a display board with two pictures attached. On one was a bulls-eye. On the other was the sketch of a human face. This board was hung in a chamber where a baby could lie safely underneath and see both images. Then, from behind the board, invisible to the baby, he peeked through a hole to watch what the baby looked at. This study showed that a two-month old baby looked twice as much at the human face as it did at the bulls-eye. This suggests that human babies have some powers of pattern and form selection. Before this experiment it was thought that babies looked out onto a chaotic world of which they could make little sense.

7. Hawthorne Effect

Study conducted by: henry a. landsberger.

Study Conducted in 1955 at Hawthorne Works in Chicago, Illinois

Landsberger performed the study by analyzing data from experiments conducted between 1924 and 1932, by Elton Mayo, at the Hawthorne Works near Chicago. The company had commissioned studies to evaluate whether the level of light in a building changed the productivity of the workers. What Mayo found was that the level of light made no difference in productivity. The workers increased their output whenever the amount of light was switched from a low level to a high level, or vice versa.

The researchers noticed a tendency that the workers’ level of efficiency increased when any variable was manipulated. The study showed that the output changed simply because the workers were aware that they were under observation. The conclusion was that the workers felt important because they were pleased to be singled out. They increased productivity as a result. Being singled out was the factor dictating increased productivity, not the changing lighting levels, or any of the other factors that they experimented upon.

The Hawthorne Effect has become one of the hardest inbuilt biases to eliminate or factor into the design of any experiment in psychology and beyond.

8. Kitty Genovese Case

Study conducted by: new york police force.

Study Conducted in 1964 in New York City

Experiment Details: The murder case of Kitty Genovese was never intended to be a psychological experiment, however it ended up having serious implications for the field.

According to a New York Times article, almost 40 neighbors witnessed Kitty Genovese being savagely attacked and murdered in Queens, New York in 1964. Not one neighbor called the police for help. Some reports state that the attacker briefly left the scene and later returned to “finish off” his victim. It was later uncovered that many of these facts were exaggerated. (There were more likely only a dozen witnesses and records show that some calls to police were made).

What this case later become famous for is the “Bystander Effect,” which states that the more bystanders that are present in a social situation, the less likely it is that anyone will step in and help. This effect has led to changes in medicine, psychology and many other areas. One famous example is the way CPR is taught to new learners. All students in CPR courses learn that they must assign one bystander the job of alerting authorities which minimizes the chances of no one calling for assistance.

9. Learned Helplessness Experiment

Study conducted by: martin seligman.

Study Conducted in 1967 at the University of Pennsylvania

Seligman’s experiment involved the ringing of a bell and then the administration of a light shock to a dog. After a number of pairings, the dog reacted to the shock even before it happened. As soon as the dog heard the bell, he reacted as though he’d already been shocked.

During the course of this study something unexpected happened. Each dog was placed in a large crate that was divided down the middle with a low fence. The dog could see and jump over the fence easily. The floor on one side of the fence was electrified, but not on the other side of the fence. Seligman placed each dog on the electrified side and administered a light shock. He expected the dog to jump to the non-shocking side of the fence. In an unexpected turn, the dogs simply laid down.

The hypothesis was that as the dogs learned from the first part of the experiment that there was nothing they could do to avoid the shocks, they gave up in the second part of the experiment. To prove this hypothesis the experimenters brought in a new set of animals and found that dogs with no history in the experiment would jump over the fence.

This condition was described as learned helplessness. A human or animal does not attempt to get out of a negative situation because the past has taught them that they are helpless.

10. Little Albert Experiment

Study conducted by: john b. watson and rosalie rayner.

Study Conducted in 1920 at Johns Hopkins University

The experiment began by placing a white rat in front of the infant, who initially had no fear of the animal. Watson then produced a loud sound by striking a steel bar with a hammer every time little Albert was presented with the rat. After several pairings (the noise and the presentation of the white rat), the boy began to cry and exhibit signs of fear every time the rat appeared in the room. Watson also created similar conditioned reflexes with other common animals and objects (rabbits, Santa beard, etc.) until Albert feared them all.

This study proved that classical conditioning works on humans. One of its most important implications is that adult fears are often connected to early childhood experiences.

11. Magical Number Seven

Study conducted by: george a. miller.

Study Conducted in 1956 at Princeton University

Experiment Details:   Frequently referred to as “ Miller’s Law,” the Magical Number Seven experiment purports that the number of objects an average human can hold in working memory is 7 ± 2. This means that the human memory capacity typically includes strings of words or concepts ranging from 5-9. This information on the limits to the capacity for processing information became one of the most highly cited papers in psychology.

The Magical Number Seven Experiment was published in 1956 by cognitive psychologist George A. Miller of Princeton University’s Department of Psychology in Psychological Review .  In the article, Miller discussed a concurrence between the limits of one-dimensional absolute judgment and the limits of short-term memory.

In a one-dimensional absolute-judgment task, a person is presented with a number of stimuli that vary on one dimension (such as 10 different tones varying only in pitch). The person responds to each stimulus with a corresponding response (learned before).

Performance is almost perfect up to five or six different stimuli but declines as the number of different stimuli is increased. This means that a human’s maximum performance on one-dimensional absolute judgment can be described as an information store with the maximum capacity of approximately 2 to 3 bits of information There is the ability to distinguish between four and eight alternatives.

12. Pavlov’s Dog Experiment

Study conducted by: ivan pavlov.

Study Conducted in the 1890s at the Military Medical Academy in St. Petersburg, Russia

Pavlov began with the simple idea that there are some things that a dog does not need to learn. He observed that dogs do not learn to salivate when they see food. This reflex is “hard wired” into the dog. This is an unconditioned response (a stimulus-response connection that required no learning).

Pavlov outlined that there are unconditioned responses in the animal by presenting a dog with a bowl of food and then measuring its salivary secretions. In the experiment, Pavlov used a bell as his neutral stimulus. Whenever he gave food to his dogs, he also rang a bell. After a number of repeats of this procedure, he tried the bell on its own. What he found was that the bell on its own now caused an increase in salivation. The dog had learned to associate the bell and the food. This learning created a new behavior. The dog salivated when he heard the bell. Because this response was learned (or conditioned), it is called a conditioned response. The neutral stimulus has become a conditioned stimulus.

This theory came to be known as classical conditioning.

13. Robbers Cave Experiment

Study conducted by: muzafer and carolyn sherif.

Study Conducted in 1954 at the University of Oklahoma

Experiment Details: This experiment, which studied group conflict, is considered by most to be outside the lines of what is considered ethically sound.

In 1954 researchers at the University of Oklahoma assigned 22 eleven- and twelve-year-old boys from similar backgrounds into two groups. The two groups were taken to separate areas of a summer camp facility where they were able to bond as social units. The groups were housed in separate cabins and neither group knew of the other’s existence for an entire week. The boys bonded with their cabin mates during that time. Once the two groups were allowed to have contact, they showed definite signs of prejudice and hostility toward each other even though they had only been given a very short time to develop their social group. To increase the conflict between the groups, the experimenters had them compete against each other in a series of activities. This created even more hostility and eventually the groups refused to eat in the same room. The final phase of the experiment involved turning the rival groups into friends. The fun activities the experimenters had planned like shooting firecrackers and watching movies did not initially work, so they created teamwork exercises where the two groups were forced to collaborate. At the end of the experiment, the boys decided to ride the same bus home, demonstrating that conflict can be resolved and prejudice overcome through cooperation.

Many critics have compared this study to Golding’s Lord of the Flies novel as a classic example of prejudice and conflict resolution.

14. Ross’ False Consensus Effect Study

Study conducted by: lee ross.

Study Conducted in 1977 at Stanford University

Experiment Details: In 1977, a social psychology professor at Stanford University named Lee Ross conducted an experiment that, in lay terms, focuses on how people can incorrectly conclude that others think the same way they do, or form a “false consensus” about the beliefs and preferences of others. Ross conducted the study in order to outline how the “false consensus effect” functions in humans.

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In the first part of the study, participants were asked to read about situations in which a conflict occurred and then were told two alternative ways of responding to the situation. They were asked to do three things:

• Guess which option other people would choose
• Say which option they themselves would choose
• Describe the attributes of the person who would likely choose each of the two options

What the study showed was that most of the subjects believed that other people would do the same as them, regardless of which of the two responses they actually chose themselves. This phenomenon is referred to as the false consensus effect, where an individual thinks that other people think the same way they do when they may not. The second observation coming from this important study is that when participants were asked to describe the attributes of the people who will likely make the choice opposite of their own, they made bold and sometimes negative predictions about the personalities of those who did not share their choice.

15. The Schacter and Singer Experiment on Emotion

Study conducted by: stanley schachter and jerome e. singer.

Study Conducted in 1962 at Columbia University

Experiment Details: In 1962 Schachter and Singer conducted a ground breaking experiment to prove their theory of emotion.

In the study, a group of 184 male participants were injected with epinephrine, a hormone that induces arousal including increased heartbeat, trembling, and rapid breathing. The research participants were told that they were being injected with a new medication to test their eyesight. The first group of participants was informed the possible side effects that the injection might cause while the second group of participants were not. The participants were then placed in a room with someone they thought was another participant, but was actually a confederate in the experiment. The confederate acted in one of two ways: euphoric or angry. Participants who had not been informed about the effects of the injection were more likely to feel either happier or angrier than those who had been informed.

What Schachter and Singer were trying to understand was the ways in which cognition or thoughts influence human emotion. Their study illustrates the importance of how people interpret their physiological states, which form an important component of your emotions. Though their cognitive theory of emotional arousal dominated the field for two decades, it has been criticized for two main reasons: the size of the effect seen in the experiment was not that significant and other researchers had difficulties repeating the experiment.

16. Selective Attention / Invisible Gorilla Experiment

Study conducted by: daniel simons and christopher chabris.

Study Conducted in 1999 at Harvard University

Experiment Details: In 1999 Simons and Chabris conducted their famous awareness test at Harvard University.

Participants in the study were asked to watch a video and count how many passes occurred between basketball players on the white team. The video moves at a moderate pace and keeping track of the passes is a relatively easy task. What most people fail to notice amidst their counting is that in the middle of the test, a man in a gorilla suit walked onto the court and stood in the center before walking off-screen.

The study found that the majority of the subjects did not notice the gorilla at all, proving that humans often overestimate their ability to effectively multi-task. What the study set out to prove is that when people are asked to attend to one task, they focus so strongly on that element that they may miss other important details.

17. Stanford Prison Study

Study conducted by philip zimbardo.

Study Conducted in 1971 at Stanford University

The Stanford Prison Experiment was designed to study behavior of “normal” individuals when assigned a role of prisoner or guard. College students were recruited to participate. They were assigned roles of “guard” or “inmate.”  Zimbardo played the role of the warden. The basement of the psychology building was the set of the prison. Great care was taken to make it look and feel as realistic as possible.

The prison guards were told to run a prison for two weeks. They were told not to physically harm any of the inmates during the study. After a few days, the prison guards became very abusive verbally towards the inmates. Many of the prisoners became submissive to those in authority roles. The Stanford Prison Experiment inevitably had to be cancelled because some of the participants displayed troubling signs of breaking down mentally.

Although the experiment was conducted very unethically, many psychologists believe that the findings showed how much human behavior is situational. People will conform to certain roles if the conditions are right. The Stanford Prison Experiment remains one of the most famous psychology experiments of all time.

18. Stanley Milgram Experiment

Study conducted by stanley milgram.

Study Conducted in 1961 at Stanford University

Experiment Details: This 1961 study was conducted by Yale University psychologist Stanley Milgram. It was designed to measure people’s willingness to obey authority figures when instructed to perform acts that conflicted with their morals. The study was based on the premise that humans will inherently take direction from authority figures from very early in life.

Participants were told they were participating in a study on memory. They were asked to watch another person (an actor) do a memory test. They were instructed to press a button that gave an electric shock each time the person got a wrong answer. (The actor did not actually receive the shocks, but pretended they did).

Participants were told to play the role of “teacher” and administer electric shocks to “the learner,” every time they answered a question incorrectly. The experimenters asked the participants to keep increasing the shocks. Most of them obeyed even though the individual completing the memory test appeared to be in great pain. Despite these protests, many participants continued the experiment when the authority figure urged them to. They increased the voltage after each wrong answer until some eventually administered what would be lethal electric shocks.

This experiment showed that humans are conditioned to obey authority and will usually do so even if it goes against their natural morals or common sense.

19. Surrogate Mother Experiment

Study conducted by: harry harlow.

Study Conducted from 1957-1963 at the University of Wisconsin

Experiment Details: In a series of controversial experiments during the late 1950s and early 1960s, Harry Harlow studied the importance of a mother’s love for healthy childhood development.

In order to do this he separated infant rhesus monkeys from their mothers a few hours after birth and left them to be raised by two “surrogate mothers.” One of the surrogates was made of wire with an attached bottle for food. The other was made of soft terrycloth but lacked food. The researcher found that the baby monkeys spent much more time with the cloth mother than the wire mother, thereby proving that affection plays a greater role than sustenance when it comes to childhood development. They also found that the monkeys that spent more time cuddling the soft mother grew up to healthier.

This experiment showed that love, as demonstrated by physical body contact, is a more important aspect of the parent-child bond than the provision of basic needs. These findings also had implications in the attachment between fathers and their infants when the mother is the source of nourishment.

20. The Good Samaritan Experiment

Study conducted by: john darley and daniel batson.

Study Conducted in 1973 at The Princeton Theological Seminary (Researchers were from Princeton University)

Experiment Details: In 1973, an experiment was created by John Darley and Daniel Batson, to investigate the potential causes that underlie altruistic behavior. The researchers set out three hypotheses they wanted to test:

• People thinking about religion and higher principles would be no more inclined to show helping behavior than laymen.
• People in a rush would be much less likely to show helping behavior.
• People who are religious for personal gain would be less likely to help than people who are religious because they want to gain some spiritual and personal insights into the meaning of life.

Student participants were given some religious teaching and instruction. They were then were told to travel from one building to the next. Between the two buildings was a man lying injured and appearing to be in dire need of assistance. The first variable being tested was the degree of urgency impressed upon the subjects, with some being told not to rush and others being informed that speed was of the essence.

The results of the experiment were intriguing, with the haste of the subject proving to be the overriding factor. When the subject was in no hurry, nearly two-thirds of people stopped to lend assistance. When the subject was in a rush, this dropped to one in ten.

People who were on the way to deliver a speech about helping others were nearly twice as likely to help as those delivering other sermons,. This showed that the thoughts of the individual were a factor in determining helping behavior. Religious beliefs did not appear to make much difference on the results. Being religious for personal gain, or as part of a spiritual quest, did not appear to make much of an impact on the amount of helping behavior shown.

21. The Halo Effect Experiment

Study conducted by: richard e. nisbett and timothy decamp wilson.

Study Conducted in 1977 at the University of Michigan

Experiment Details: The Halo Effect states that people generally assume that people who are physically attractive are more likely to:

• be intelligent
• be friendly
• display good judgment

To prove their theory, Nisbett and DeCamp Wilson created a study to prove that people have little awareness of the nature of the Halo Effect. They’re not aware that it influences:

• their personal judgments
• the production of a more complex social behavior

In the experiment, college students were the research participants. They were asked to evaluate a psychology instructor as they view him in a videotaped interview. The students were randomly assigned to one of two groups. Each group was shown one of two different interviews with the same instructor. The instructor is a native French-speaking Belgian who spoke English with a noticeable accent. In the first video, the instructor presented himself as someone:

• respectful of his students’ intelligence and motives
• flexible in his approach to teaching
• enthusiastic about his subject matter

In the second interview, he presented himself as much more unlikable. He was cold and distrustful toward the students and was quite rigid in his teaching style.

After watching the videos, the subjects were asked to rate the lecturer on:

• physical appearance

His mannerisms and accent were kept the same in both versions of videos. The subjects were asked to rate the professor on an 8-point scale ranging from “like extremely” to “dislike extremely.” Subjects were also told that the researchers were interested in knowing “how much their liking for the teacher influenced the ratings they just made.” Other subjects were asked to identify how much the characteristics they just rated influenced their liking of the teacher.

After responding to the questionnaire, the respondents were puzzled about their reactions to the videotapes and to the questionnaire items. The students had no idea why they gave one lecturer higher ratings. Most said that how much they liked the lecturer had not affected their evaluation of his individual characteristics at all.

The interesting thing about this study is that people can understand the phenomenon, but they are unaware when it is occurring. Without realizing it, humans make judgments. Even when it is pointed out, they may still deny that it is a product of the halo effect phenomenon.

22. The Marshmallow Test

Study conducted by: walter mischel.

Study Conducted in 1972 at Stanford University

In his 1972 Marshmallow Experiment, children ages four to six were taken into a room where a marshmallow was placed in front of them on a table. Before leaving each of the children alone in the room, the experimenter informed them that they would receive a second marshmallow if the first one was still on the table after they returned in 15 minutes. The examiner recorded how long each child resisted eating the marshmallow and noted whether it correlated with the child’s success in adulthood. A small number of the 600 children ate the marshmallow immediately and one-third delayed gratification long enough to receive the second marshmallow.

In follow-up studies, Mischel found that those who deferred gratification were significantly more competent and received higher SAT scores than their peers. This characteristic likely remains with a person for life. While this study seems simplistic, the findings outline some of the foundational differences in individual traits that can predict success.

23. The Monster Study

Study conducted by: wendell johnson.

Study Conducted in 1939 at the University of Iowa

Experiment Details: The Monster Study received this negative title due to the unethical methods that were used to determine the effects of positive and negative speech therapy on children.

Wendell Johnson of the University of Iowa selected 22 orphaned children, some with stutters and some without. The children were in two groups. The group of children with stutters was placed in positive speech therapy, where they were praised for their fluency. The non-stutterers were placed in negative speech therapy, where they were disparaged for every mistake in grammar that they made.

As a result of the experiment, some of the children who received negative speech therapy suffered psychological effects and retained speech problems for the rest of their lives. They were examples of the significance of positive reinforcement in education.

The initial goal of the study was to investigate positive and negative speech therapy. However, the implication spanned much further into methods of teaching for young children.

24. Violinist at the Metro Experiment

Study conducted by: staff at the washington post.

Study Conducted in 2007 at a Washington D.C. Metro Train Station

During the study, pedestrians rushed by without realizing that the musician playing at the entrance to the metro stop was Grammy-winning musician, Joshua Bell. Two days before playing in the subway, he sold out at a theater in Boston where the seats average $100. He played one of the most intricate pieces ever written with a violin worth 3.5 million dollars. In the 45 minutes the musician played his violin, only 6 people stopped and stayed for a while. Around 20 gave him money, but continued to walk their normal pace. He collected $32.

The study and the subsequent article organized by the Washington Post was part of a social experiment looking at:

• the priorities of people

Gene Weingarten wrote about the social experiment: “In a banal setting at an inconvenient time, would beauty transcend?” Later he won a Pulitzer Prize for his story. Some of the questions the article addresses are:

• Do we perceive beauty?
• Do we stop to appreciate it?
• Do we recognize the talent in an unexpected context?

As it turns out, many of us are not nearly as perceptive to our environment as we might like to think.

25. Visual Cliff Experiment

Study conducted by: eleanor gibson and richard walk.

Study Conducted in 1959 at Cornell University

Experiment Details: In 1959, psychologists Eleanor Gibson and Richard Walk set out to study depth perception in infants. They wanted to know if depth perception is a learned behavior or if it is something that we are born with. To study this, Gibson and Walk conducted the visual cliff experiment.

They studied 36 infants between the ages of six and 14 months, all of whom could crawl. The infants were placed one at a time on a visual cliff. A visual cliff was created using a large glass table that was raised about a foot off the floor. Half of the glass table had a checker pattern underneath in order to create the appearance of a ‘shallow side.’

In order to create a ‘deep side,’ a checker pattern was created on the floor; this side is the visual cliff. The placement of the checker pattern on the floor creates the illusion of a sudden drop-off. Researchers placed a foot-wide centerboard between the shallow side and the deep side. Gibson and Walk found the following:

• Nine of the infants did not move off the centerboard.
• All of the 27 infants who did move crossed into the shallow side when their mothers called them from the shallow side.
• Three of the infants crawled off the visual cliff toward their mother when called from the deep side.
• When called from the deep side, the remaining 24 children either crawled to the shallow side or cried because they could not cross the visual cliff and make it to their mother.

What this study helped demonstrate is that depth perception is likely an inborn train in humans.

Among these experiments and psychological tests, we see boundaries pushed and theories taking on a life of their own. It is through the endless stream of psychological experimentation that we can see simple hypotheses become guiding theories for those in this field. The greater field of psychology became a formal field of experimental study in 1879, when Wilhelm Wundt established the first laboratory dedicated solely to psychological research in Leipzig, Germany. Wundt was the first person to refer to himself as a psychologist. Since 1879, psychology has grown into a massive collection of:

• methods of practice

It’s also a specialty area in the field of healthcare. None of this would have been possible without these and many other important psychological experiments that have stood the test of time.

• 20 Most Unethical Experiments in Psychology
• What Careers are in Experimental Psychology?
• 10 Things to Know About the Psychology of Psychotherapy

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After earning a Bachelor of Arts in Psychology from Rutgers University and then a Master of Science in Clinical and Forensic Psychology from Drexel University, Kristen began a career as a therapist at two prisons in Philadelphia. At the same time she volunteered as a rape crisis counselor, also in Philadelphia. After a few years in the field she accepted a teaching position at a local college where she currently teaches online psychology courses. Kristen began writing in college and still enjoys her work as a writer, editor, professor and mother.

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People make more patient decisions when shown the benefits first

Focusing immediately on the benefits of waiting might help people improve their self-control.

If you had to decide whether to receive $40 in seven days or $60 in 30 days, which would you choose? Your answer could have less to do with whether you are a patient or impatient person than with how the choice is presented, according to a new paper published in Nature Communications .

The research found that first revealing the time delay -- seven to 30 days -- made people tend to prefer the shorter-term, "impatient" option, while first revealing the greater reward of the 30-day option encouraged people to choose the "patient" option of waiting to receive more money. The amount of time allotted to decide also influences their choices, but not always in the way you might expect. In some cases, people were more patient when they had less time to decide.

"The takeaway message is that people can be impatient or exhibit a lack of self-control for many reasons," said corresponding author Ian Krajbich, an associate professor of psychology at UCLA. "It may in part reflect their true patience but it may also be due to attentional biases, like how prominently delay information is presented. Immediately focusing on the benefits of waiting might help people improve their self-control."

Krajbich, who studies the cognitive process by which people make choices, and colleagues at Zhejiang University and Hangzhou Normal University, led by Fadong Chen, asked a total of 353 college student volunteers to choose between patient and impatient alternatives, for example to receive $40 in seven days or $60 in 30 days, by clicking their choice on a computer screen while software tracked and recorded the movements of their mouse. In some cases, participants had to make their decisions in two seconds, in others they had unlimited time or had to wait 10 seconds before choosing. At the end of the study, participants earned money based on one decision.

Whether the mouse shot straight to one of the options or wandered a little as the participant considered their options revealed the order in which they were considering dimensions of the task, and at what point in time their mouse movements were first influenced by either the delays or rewards.

More than half the participants patiently chose the "larger later" option regardless of time constraint:

• Surprisingly, when given the least time to think about it, they made the most patient decisions. With just two seconds to choose, 65% opted for the "larger later" option.
• With unlimited time, 59% chose the "larger later" option, as did only 54% of those who had to wait 10 seconds before choosing.
• But participants who generally favored the "smaller sooner" options showed the opposite pattern, tending to prefer the "larger later" option when they had more time to think about it.

"If you're somebody who focuses on the rewards first, time pressure accentuates that and makes you more patient," Krajbich said. "And if you're a little impatient by nature and focus on delays first, time pressure magnifies that impatience. Time pressure has different effects for different people. It enhances inherent bias."

But the researchers found that they could manipulate that bias by changing how they presented information about the choices.

The researchers then repeated the experiments, but altered how the information was presented, sometimes revealing the delay first and sometimes revealing the rewards first. In these experiments, participants were allowed to make choices at various times, such as after seeing just one piece of information or after seeing them all.

These experiments revealed that when shown the rewards first, participants made more "larger later" choices. When the time delay was presented first, they made more "smaller sooner" choices. People were more patient when they saw rewards before delays.

Research on decision-making has shown that when people are making decisions, they have to evaluate their options over time because they often don't immediately know what to do. Because people have limited attention, they tend to focus on one dimension of the choice at a time.

In the experiments, these two dimensions were delay or reward, and participants tended to consider the amounts first and then the delays, but this varied across people. Those who were less patient in their choices were more likely to consider the delays first.

"If people consider amounts first, they're more likely to choose the patient option, and if they consider the delays first, they're more likely to choose the impatient option. If you're trying to get people to be more patient by getting them to slow down or speed up their decisions, you need to know which dimension they're going to focus on first. That will determine the appropriate intervention," Krajbich said.

The findings could be applied where people are being encouraged to make life choices that will benefit them in the long run, such as eating healthier, exercising or saving for retirement.

"You want to emphasize those future large rewards and try to deemphasize how long it's going to take," Krajbich said. "Try to have the reward information come first."

• Consumer Behavior
• Racial Issues
• Disorders and Syndromes
• Gender Difference
• The Long Tail
• Illusion of control
• Microeconomics
• Milgram experiment
• Delayed sleep phase syndrome
• Social psychology

Story Source:

Materials provided by University of California - Los Angeles . Original written by Holly Ober. Note: Content may be edited for style and length.

Journal Reference :

• Fadong Chen, Jiehui Zheng, Lei Wang, Ian Krajbich. Attribute latencies causally shape intertemporal decisions . Nature Communications , 2024; 15 (1) DOI: 10.1038/s41467-024-46657-2

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Chapter 6: Experimental Research

6.1 experiment basics, learning objectives.

• Explain what an experiment is and recognize examples of studies that are experiments and studies that are not experiments.
• Explain what internal validity is and why experiments are considered to be high in internal validity.
• Explain what external validity is and evaluate studies in terms of their external validity.
• Distinguish between the manipulation of the independent variable and control of extraneous variables and explain the importance of each.
• Recognize examples of confounding variables and explain how they affect the internal validity of a study.

What Is an Experiment?

As we saw earlier in the book, an experiment is a type of study designed specifically to answer the question of whether there is a causal relationship between two variables. Do changes in an independent variable cause changes in a dependent variable? Experiments have two fundamental features. The first is that the researchers manipulate, or systematically vary, the level of the independent variable. The different levels of the independent variable are called conditions. For example, in Darley and Latané’s experiment, the independent variable was the number of witnesses that participants believed to be present. The researchers manipulated this independent variable by telling participants that there were either one, two, or five other students involved in the discussion, thereby creating three conditions. The second fundamental feature of an experiment is that the researcher controls, or minimizes the variability in, variables other than the independent and dependent variable. These other variables are called extraneous variables. Darley and Latané tested all their participants in the same room, exposed them to the same emergency situation, and so on. They also randomly assigned their participants to conditions so that the three groups would be similar to each other to begin with. Notice that although the words manipulation and control have similar meanings in everyday language, researchers make a clear distinction between them. They manipulate the independent variable by systematically changing its levels and control other variables by holding them constant.

Internal and External Validity

Internal validity.

Recall that the fact that two variables are statistically related does not necessarily mean that one causes the other. “Correlation does not imply causation.” For example, if it were the case that people who exercise regularly are happier than people who do not exercise regularly, this would not necessarily mean that exercising increases people’s happiness. It could mean instead that greater happiness causes people to exercise (the directionality problem) or that something like better physical health causes people to exercise and be happier (the third-variable problem).

The purpose of an experiment, however, is to show that two variables are statistically related and to do so in a way that supports the conclusion that the independent variable caused any observed differences in the dependent variable. The basic logic is this: If the researcher creates two or more highly similar conditions and then manipulates the independent variable to produce just one difference between them, then any later difference between the conditions must have been caused by the independent variable. For example, because the only difference between Darley and Latané’s conditions was the number of students that participants believed to be involved in the discussion, this must have been responsible for differences in helping between the conditions.

An empirical study is said to be high in internal validity if the way it was conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Thus experiments are high in internal validity because the way they are conducted—with the manipulation of the independent variable and the control of extraneous variables—provides strong support for causal conclusions.

External Validity

At the same time, the way that experiments are conducted sometimes leads to a different kind of criticism. Specifically, the need to manipulate the independent variable and control extraneous variables means that experiments are often conducted under conditions that seem artificial or unlike “real life” (Stanovich, 2010). In many psychology experiments, the participants are all college undergraduates and come to a classroom or laboratory to fill out a series of paper-and-pencil questionnaires or to perform a carefully designed computerized task. Consider, for example, an experiment in which researcher Barbara Fredrickson and her colleagues had college students come to a laboratory on campus and complete a math test while wearing a swimsuit (Fredrickson, Roberts, Noll, Quinn, & Twenge, 1998). At first, this might seem silly. When will college students ever have to complete math tests in their swimsuits outside of this experiment?

The issue we are confronting is that of external validity. An empirical study is high in external validity if the way it was conducted supports generalizing the results to people and situations beyond those actually studied. As a general rule, studies are higher in external validity when the participants and the situation studied are similar to those that the researchers want to generalize to. Imagine, for example, that a group of researchers is interested in how shoppers in large grocery stores are affected by whether breakfast cereal is packaged in yellow or purple boxes. Their study would be high in external validity if they studied the decisions of ordinary people doing their weekly shopping in a real grocery store. If the shoppers bought much more cereal in purple boxes, the researchers would be fairly confident that this would be true for other shoppers in other stores. Their study would be relatively low in external validity, however, if they studied a sample of college students in a laboratory at a selective college who merely judged the appeal of various colors presented on a computer screen. If the students judged purple to be more appealing than yellow, the researchers would not be very confident that this is relevant to grocery shoppers’ cereal-buying decisions.

We should be careful, however, not to draw the blanket conclusion that experiments are low in external validity. One reason is that experiments need not seem artificial. Consider that Darley and Latané’s experiment provided a reasonably good simulation of a real emergency situation. Or consider field experiments that are conducted entirely outside the laboratory. In one such experiment, Robert Cialdini and his colleagues studied whether hotel guests choose to reuse their towels for a second day as opposed to having them washed as a way of conserving water and energy (Cialdini, 2005). These researchers manipulated the message on a card left in a large sample of hotel rooms. One version of the message emphasized showing respect for the environment, another emphasized that the hotel would donate a portion of their savings to an environmental cause, and a third emphasized that most hotel guests choose to reuse their towels. The result was that guests who received the message that most hotel guests choose to reuse their towels reused their own towels substantially more often than guests receiving either of the other two messages. Given the way they conducted their study, it seems very likely that their result would hold true for other guests in other hotels.

A second reason not to draw the blanket conclusion that experiments are low in external validity is that they are often conducted to learn about psychological processes that are likely to operate in a variety of people and situations. Let us return to the experiment by Fredrickson and colleagues. They found that the women in their study, but not the men, performed worse on the math test when they were wearing swimsuits. They argued that this was due to women’s greater tendency to objectify themselves—to think about themselves from the perspective of an outside observer—which diverts their attention away from other tasks. They argued, furthermore, that this process of self-objectification and its effect on attention is likely to operate in a variety of women and situations—even if none of them ever finds herself taking a math test in her swimsuit.

Manipulation of the Independent Variable

Again, to manipulate an independent variable means to change its level systematically so that different groups of participants are exposed to different levels of that variable, or the same group of participants is exposed to different levels at different times. For example, to see whether expressive writing affects people’s health, a researcher might instruct some participants to write about traumatic experiences and others to write about neutral experiences. The different levels of the independent variable are referred to as conditions , and researchers often give the conditions short descriptive names to make it easy to talk and write about them. In this case, the conditions might be called the “traumatic condition” and the “neutral condition.”

Notice that the manipulation of an independent variable must involve the active intervention of the researcher. Comparing groups of people who differ on the independent variable before the study begins is not the same as manipulating that variable. For example, a researcher who compares the health of people who already keep a journal with the health of people who do not keep a journal has not manipulated this variable and therefore not conducted an experiment. This is important because groups that already differ in one way at the beginning of a study are likely to differ in other ways too. For example, people who choose to keep journals might also be more conscientious, more introverted, or less stressed than people who do not. Therefore, any observed difference between the two groups in terms of their health might have been caused by whether or not they keep a journal, or it might have been caused by any of the other differences between people who do and do not keep journals. Thus the active manipulation of the independent variable is crucial for eliminating the third-variable problem.

Of course, there are many situations in which the independent variable cannot be manipulated for practical or ethical reasons and therefore an experiment is not possible. For example, whether or not people have a significant early illness experience cannot be manipulated, making it impossible to do an experiment on the effect of early illness experiences on the development of hypochondriasis. This does not mean it is impossible to study the relationship between early illness experiences and hypochondriasis—only that it must be done using nonexperimental approaches. We will discuss this in detail later in the book.

In many experiments, the independent variable is a construct that can only be manipulated indirectly. For example, a researcher might try to manipulate participants’ stress levels indirectly by telling some of them that they have five minutes to prepare a short speech that they will then have to give to an audience of other participants. In such situations, researchers often include a manipulation check in their procedure. A manipulation check is a separate measure of the construct the researcher is trying to manipulate. For example, researchers trying to manipulate participants’ stress levels might give them a paper-and-pencil stress questionnaire or take their blood pressure—perhaps right after the manipulation or at the end of the procedure—to verify that they successfully manipulated this variable.

Control of Extraneous Variables

An extraneous variable is anything that varies in the context of a study other than the independent and dependent variables. In an experiment on the effect of expressive writing on health, for example, extraneous variables would include participant variables (individual differences) such as their writing ability, their diet, and their shoe size. They would also include situation or task variables such as the time of day when participants write, whether they write by hand or on a computer, and the weather. Extraneous variables pose a problem because many of them are likely to have some effect on the dependent variable. For example, participants’ health will be affected by many things other than whether or not they engage in expressive writing. This can make it difficult to separate the effect of the independent variable from the effects of the extraneous variables, which is why it is important to control extraneous variables by holding them constant.

Extraneous Variables as “Noise”

Extraneous variables make it difficult to detect the effect of the independent variable in two ways. One is by adding variability or “noise” to the data. Imagine a simple experiment on the effect of mood (happy vs. sad) on the number of happy childhood events people are able to recall. Participants are put into a negative or positive mood (by showing them a happy or sad video clip) and then asked to recall as many happy childhood events as they can. The two leftmost columns of Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” show what the data might look like if there were no extraneous variables and the number of happy childhood events participants recalled was affected only by their moods. Every participant in the happy mood condition recalled exactly four happy childhood events, and every participant in the sad mood condition recalled exactly three. The effect of mood here is quite obvious. In reality, however, the data would probably look more like those in the two rightmost columns of Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” . Even in the happy mood condition, some participants would recall fewer happy memories because they have fewer to draw on, use less effective strategies, or are less motivated. And even in the sad mood condition, some participants would recall more happy childhood memories because they have more happy memories to draw on, they use more effective recall strategies, or they are more motivated. Although the mean difference between the two groups is the same as in the idealized data, this difference is much less obvious in the context of the greater variability in the data. Thus one reason researchers try to control extraneous variables is so their data look more like the idealized data in Table 6.1 “Hypothetical Noiseless Data and Realistic Noisy Data” , which makes the effect of the independent variable is easier to detect (although real data never look quite that good).

Table 6.1 Hypothetical Noiseless Data and Realistic Noisy Data

One way to control extraneous variables is to hold them constant. This can mean holding situation or task variables constant by testing all participants in the same location, giving them identical instructions, treating them in the same way, and so on. It can also mean holding participant variables constant. For example, many studies of language limit participants to right-handed people, who generally have their language areas isolated in their left cerebral hemispheres. Left-handed people are more likely to have their language areas isolated in their right cerebral hemispheres or distributed across both hemispheres, which can change the way they process language and thereby add noise to the data.

In principle, researchers can control extraneous variables by limiting participants to one very specific category of person, such as 20-year-old, straight, female, right-handed, sophomore psychology majors. The obvious downside to this approach is that it would lower the external validity of the study—in particular, the extent to which the results can be generalized beyond the people actually studied. For example, it might be unclear whether results obtained with a sample of younger straight women would apply to older gay men. In many situations, the advantages of a diverse sample outweigh the reduction in noise achieved by a homogeneous one.

Extraneous Variables as Confounding Variables

The second way that extraneous variables can make it difficult to detect the effect of the independent variable is by becoming confounding variables. A confounding variable is an extraneous variable that differs on average across levels of the independent variable. For example, in almost all experiments, participants’ intelligence quotients (IQs) will be an extraneous variable. But as long as there are participants with lower and higher IQs at each level of the independent variable so that the average IQ is roughly equal, then this variation is probably acceptable (and may even be desirable). What would be bad, however, would be for participants at one level of the independent variable to have substantially lower IQs on average and participants at another level to have substantially higher IQs on average. In this case, IQ would be a confounding variable.

To confound means to confuse, and this is exactly what confounding variables do. Because they differ across conditions—just like the independent variable—they provide an alternative explanation for any observed difference in the dependent variable. Figure 6.1 “Hypothetical Results From a Study on the Effect of Mood on Memory” shows the results of a hypothetical study, in which participants in a positive mood condition scored higher on a memory task than participants in a negative mood condition. But if IQ is a confounding variable—with participants in the positive mood condition having higher IQs on average than participants in the negative mood condition—then it is unclear whether it was the positive moods or the higher IQs that caused participants in the first condition to score higher. One way to avoid confounding variables is by holding extraneous variables constant. For example, one could prevent IQ from becoming a confounding variable by limiting participants only to those with IQs of exactly 100. But this approach is not always desirable for reasons we have already discussed. A second and much more general approach—random assignment to conditions—will be discussed in detail shortly.

Figure 6.1 Hypothetical Results From a Study on the Effect of Mood on Memory

Because IQ also differs across conditions, it is a confounding variable.

Key Takeaways

• An experiment is a type of empirical study that features the manipulation of an independent variable, the measurement of a dependent variable, and control of extraneous variables.
• Studies are high in internal validity to the extent that the way they are conducted supports the conclusion that the independent variable caused any observed differences in the dependent variable. Experiments are generally high in internal validity because of the manipulation of the independent variable and control of extraneous variables.
• Studies are high in external validity to the extent that the result can be generalized to people and situations beyond those actually studied. Although experiments can seem “artificial”—and low in external validity—it is important to consider whether the psychological processes under study are likely to operate in other people and situations.
• Practice: List five variables that can be manipulated by the researcher in an experiment. List five variables that cannot be manipulated by the researcher in an experiment.

Practice: For each of the following topics, decide whether that topic could be studied using an experimental research design and explain why or why not.

• Effect of parietal lobe damage on people’s ability to do basic arithmetic.
• Effect of being clinically depressed on the number of close friendships people have.
• Effect of group training on the social skills of teenagers with Asperger’s syndrome.
• Effect of paying people to take an IQ test on their performance on that test.

Cialdini, R. (2005, April). Don’t throw in the towel: Use social influence research. APS Observer . Retrieved from http://www.psychologicalscience.org/observer/getArticle.cfm?id=1762 .

Fredrickson, B. L., Roberts, T.-A., Noll, S. M., Quinn, D. M., & Twenge, J. M. (1998). The swimsuit becomes you: Sex differences in self-objectification, restrained eating, and math performance. Journal of Personality and Social Psychology, 75 , 269–284.

Stanovich, K. E. (2010). How to think straight about psychology (9th ed.). Boston, MA: Allyn & Bacon.

• Research Methods in Psychology. Provided by : University of Minnesota Libraries Publishing. Located at : http://open.lib.umn.edu/psychologyresearchmethods . License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

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Pavlov and the Kingdom of Dogs

Storying experimental animal histories through arts-based research.

• Press and publications
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• Why Pavlov’s Research (& his Dogs) Still Matter

Image source: Matthew Adams

Pavlov’s conditioning experiments with dogs are often discussed in Psychology and remain influential.

This is partly because of their foundational role in shaping our understanding of learning and behaviour. His work introduced the concept of ‘classical conditioning’, and underpinned models about the physiological basis of psychological processes and the nature of learning that remain influential today in fields such as psychology, neuroscience, and behavioural therapy. Beyond academia, the societal implications of these and later conditioning experiments have long been recognised, contributing to fields like marketing, advertising and social influence.

Despite the undoubtedly important legacy of his work, a primary aim for us in creating our exhibition Pavlov & the Kingdom of Dogs was to spotlight a lesser-known element – the experiences of Pavlov’s dogs . We have used arts-based methods to do so, creating scale models to explore their living conditions, relationships, and the nature of their involvement in experiments, including moments of resistance, whilst locating them within specific historical and geographical context.

Why such an emphasis on experimental animals? Another claim regarding Pavlov’s ongoing influence is that his experiments also sparked discussions on ethical considerations in animal research that have continued to this day. The usual story here is that Pavlov was a pioneer in taking seriously the welfare of his animals, but also that ethical concerns raised during his time have been key to subsequent progress – not least the development of ethical guidelines for animal experimentation that shape research practices today.  However, Pavlov & the Kingdom of Dogs  seeks to challenge conventional perceptions of animal experimentation, the nature of scientific work, and the history of Psychology. In doing so the exhibition is intended as a kind of ‘history from below’. According to the Institute of Historical Research

History from below seeks to take as its subjects ordinary people, and concentrate on their experiences and perspectives, contrasting itself with the stereotype of traditional political history and its focus on the actions of ‘great men’.

Image source: ‘ Teach History from Below ’ by Shaun Slifer

We do something very similar, taking as our subject ordinary animals . By emphasising the experiences and agency of experimental animals, we hope to follow a ‘history from below’ tradition of challenging dominant historical narratives and taken-for-granted assumptions, in this case about the experiences and agency of animals involved in experiments.

Why does contributing to changing the idea of what, or who, an experimental animal is historically still matter today ? Ethical issues in research involving animals have not disappeared as a result of the development of ethical governance and guidelines. As we learn more about the intelligence and complexity of non-human animals, what counts as suitable practice shifts, informing a growing cultural conversation about the depth of non-human animal awareness and abilities, the intricate interdependence between humans and other species, and the need to develop sensibilities rooted in awareness and respect for all forms of life.

In psychology and behavioural science, this is reflected in calls to update ethical review practices and research design to incorporate the naming of animals, understanding of an individual animal’s experience of an experiment, and information about how animals are recruited, housed, handled and fed; what was required of them during experiments; their life expectancy; and other aspects of their lives outside of experiments.  Psychologists also increasingly work with animals outside of the traditional lab environment, designing, delivering and/or evaluating note the increasing range of animal-assisted interventions and therapies – support and companion animals, cat cafes, equestrian-assisted therapy, cow cuddling, and care farms to name but a few. All of these interventions raise ethical and welfare issues for psychologists and other interested parties to address.

More generally, we still live in a world in which animal lives, and human-animal relationships and encounters, are not just central but highly organised and structured, from industrial animal agriculture to the sport, leisure and entertainment industries. Just as with contemporary research involving animals, in all these areas problematic practices continue to be highlighted, and changes demanded, ranging from reform to abolition. Considering these issues as contemporary and ongoing, we hope then that our exhibition can contribute to discussion about the role of animals in society and culture today .  It has never been more important for us to pay close attention to the experiences, rights and welfare of the animals involved.

Matthew Adams

Dr Matthew Adams is a Chartered Psychologist and Principal Lecturer in Psychology in the School of Applied Social Sciences. His teaching and research is predominantly in the fields of social and environmental psychology.

March 12, 2024

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Classic Psychology Experiments

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Emily is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, Vox, and Verywell.

The history of psychology is filled with fascinating studies and classic psychology experiments that helped change the way we think about ourselves and human behavior. Sometimes the results of these experiments were so surprising they challenged conventional wisdom about the human mind and actions. In other cases, these experiments were also quite controversial.

Some of the most famous examples include Milgram's obedience experiment and Zimbardo's prison experiment. Explore some of these classic psychology experiments to learn more about some of the best-known research in psychology history.

Harlow’s Rhesus Monkey Experiments

In a series of controversial experiments conducted in the late 1950s and early 1960s, psychologist Harry Harlow demonstrated the powerful effects of love on normal development. By showing the devastating effects of deprivation on young rhesus monkeys , Harlow revealed the importance of love for healthy childhood development.

His experiments were often unethical and shockingly cruel, yet they uncovered fundamental truths that have heavily influenced our understanding of child development.

In one famous version of the experiments, infant monkeys were separated from their mothers immediately after birth and placed in an environment where they had access to either a wire monkey "mother" or a version of the faux-mother covered in a soft-terry cloth. While the wire mother provided food, the cloth mother provided only softness and comfort.

Harlow found that while the infant monkeys would go to the wire mother for food, they vastly preferred the company of the soft and comforting cloth mother. The study demonstrated that maternal bonds   were about much more than simply providing nourishment and that comfort and security played a major role in the formation of attachments .

Pavlov’s Classical Conditioning Experiments

The concept of classical conditioning is studied by every entry-level psychology student, so it may be surprising to learn that the man who first noted this phenomenon was not a psychologist at all. Pavlov was actually studying the digestive systems of dogs when he noticed that his subjects began to salivate whenever they saw his lab assistant.

What he soon discovered through his experiments was that certain responses (drooling) could be conditioned by associating a previously neutral stimulus (metronome or buzzer) with a stimulus that naturally and automatically triggers a response (food). Pavlov's experiments with dogs established classical conditioning.

The Asch Conformity Experiments

Researchers have long been interested in the degree to which people follow or rebel against social norms. During the 1950s, psychologist Solomon Asch conducted a series of experiments designed to demonstrate the powers of conformity in groups.  

The study revealed that people are surprisingly susceptible to going along with the group, even when they know the group is wrong.​ In Asch's studies, students were told that they were taking a vision test and were asked to identify which of three lines was the same length as a target line.

When asked alone, the students were highly accurate in their assessments. In other trials, confederate participants intentionally picked the incorrect line. As a result, many of the real participants gave the same answer as the other students, demonstrating how conformity could be both a powerful and subtle influence on human behavior.

Skinner's Operant Conditioning Experiments

Skinner studied how behavior can be reinforced to be repeated or weakened to be extinguished. He designed the Skinner Box where an animal, often a rodent, would be given a food pellet or an electric shock. A rat would learn that pressing a level delivered a food pellet. Or the rat would learn to press the lever in order to halt electric shocks.

Then, the animal may learn to associate a light or sound with being able to get the reward or halt negative stimuli by pressing the lever. Furthermore, he studied whether continuous, fixed ratio, fixed interval , variable ratio, and variable interval reinforcement led to faster response or learning.

Milgram’s Obedience Experiments

In Milgram's experiment , participants were asked to deliver electrical shocks to a "learner" whenever an incorrect answer was given. In reality, the learner was actually a confederate in the experiment who pretended to be shocked. The purpose of the experiment was to determine how far people were willing to go in order to obey the commands of an authority figure.

Milgram  found that 65% of participants were willing to deliver the maximum level of shocks   despite the fact that the learner seemed to be in serious distress or even unconscious.

Why This Experiment Is Notable

Milgram's experiment is one of the most controversial in psychology history. Many participants experienced considerable distress as a result of their participation and in many cases were never debriefed after the conclusion of the experiment. The experiment played a role in the development of ethical guidelines for the use of human participants in psychology experiments.

The Stanford Prison Experiment

Philip Zimbardo's famous experiment cast regular students in the roles of prisoners and prison guards. While the study was originally slated to last 2 weeks, it had to be halted after just 6 days because the guards became abusive and the prisoners began to show signs of extreme stress and anxiety.

Zimbardo's famous study was referred to after the abuses in Abu Ghraib came to light. Many experts believe that such group behaviors are heavily influenced by the power of the situation and the behavioral expectations placed on people cast in different roles.

It is worth noting criticisms of Zimbardo's experiment, however. While the general recollection of the experiment is that the guards became excessively abusive on their own as a natural response to their role, the reality is that they were explicitly instructed to mistreat the prisoners, potentially detracting from the conclusions of the study.

Van rosmalen L, Van der veer R, Van der horst FCP. The nature of love: Harlow, Bowlby and Bettelheim on affectionless mothers. Hist Psychiatry. 2020. doi:10.1177/0957154X19898997

Gantt WH . Ivan Pavlov . Encyclopaedia Brittanica .

Jeon, HL. The environmental factor within the Solomon Asch Line Test . International Journal of Social Science and Humanity. 2014;4(4):264-268. doi:10.7763/IJSSH.2014.V4.360 

Koren M. B.F. Skinner: The man who taught pigeons to play ping-pong and rats to pull levers . Smithsonian Magazine .

B.F. Skinner Foundation. A brief survey of operant behavior .

Gonzalez-franco M, Slater M, Birney ME, Swapp D, Haslam SA, Reicher SD. Participant concerns for the Learner in a Virtual Reality replication of the Milgram obedience study. PLoS ONE. 2018;13(12):e0209704. doi:10.1371/journal.pone.0209704

Zimbardo PG. Philip G. Zimbardo on his career and the Stanford Prison Experiment's 40th anniversary. Interview by Scott Drury, Scott A. Hutchens, Duane E. Shuttlesworth, and Carole L. White. Hist Psychol. 2012;15(2):161-170. doi:10.1037/a0025884

Le texier T. Debunking the Stanford Prison Experiment. Am Psychol. 2019;74(7):823-839. doi:10.1037/amp0000401

Perry G. Deception and illusion in Milgram's accounts of the Obedience Experiments . Theoretical & Applied Ethics . 2013;2(2):79-92.

Specter M. Drool: How Everyone Gets Pavlov Wrong . The New Yorker. 2014; November 24.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Stanley Milgram Shock Experiment: Summary, Results, & Ethics

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

Stanley Milgram, a psychologist at Yale University, carried out one of the most famous studies of obedience in psychology.

He conducted an experiment focusing on the conflict between obedience to authority and personal conscience.

Milgram (1963) examined justifications for acts of genocide offered by those accused at the World War II, Nuremberg War Criminal trials. Their defense often was based on “ obedience ” – that they were just following orders from their superiors.

The experiments began in July 1961, a year after the trial of Adolf Eichmann in Jerusalem. Milgram devised the experiment to answer the question:

Could it be that Eichmann and his million accomplices in the Holocaust were just following orders? Could we call them all accomplices?” (Milgram, 1974).

Milgram (1963) wanted to investigate whether Germans were particularly obedient to authority figures, as this was a common explanation for the Nazi killings in World War II.

Milgram selected participants for his experiment by newspaper advertising for male participants to take part in a study of learning at Yale University.

The procedure was that the participant was paired with another person and they drew lots to find out who would be the ‘learner’ and who would be the ‘teacher.’  The draw was fixed so that the participant was always the teacher, and the learner was one of Milgram’s confederates (pretending to be a real participant).

The learner (a confederate called Mr. Wallace) was taken into a room and had electrodes attached to his arms, and the teacher and researcher went into a room next door that contained an electric shock generator and a row of switches marked from 15 volts (Slight Shock) to 375 volts (Danger: Severe Shock) to 450 volts (XXX).

The shocks in Stanley Milgram’s obedience experiments were not real. The “learners” were actors who were part of the experiment and did not actually receive any shocks.

However, the “teachers” (the real participants of the study) believed the shocks were real, which was crucial for the experiment to measure obedience to authority figures even when it involved causing harm to others.

Milgram’s Experiment (1963)

Milgram (1963) was interested in researching how far people would go in obeying an instruction if it involved harming another person.

Stanley Milgram was interested in how easily ordinary people could be influenced into committing atrocities, for example, Germans in WWII.

Volunteers were recruited for a controlled experiment investigating “learning” (re: ethics: deception). 

Participants were 40 males, aged between 20 and 50, whose jobs ranged from unskilled to professional, from the New Haven area. They were paid $4.50 for just turning up.

At the beginning of the experiment, they were introduced to another participant, a confederate of the experimenter (Milgram).

They drew straws to determine their roles – learner or teacher – although this was fixed, and the confederate was always the learner. There was also an “experimenter” dressed in a gray lab coat, played by an actor (not Milgram).

Two rooms in the Yale Interaction Laboratory were used – one for the learner (with an electric chair) and another for the teacher and experimenter with an electric shock generator.

The “learner” (Mr. Wallace) was strapped to a chair with electrodes.

After he has learned a list of word pairs given to him to learn, the “teacher” tests him by naming a word and asking the learner to recall its partner/pair from a list of four possible choices.

The teacher is told to administer an electric shock every time the learner makes a mistake, increasing the level of shock each time. There were 30 switches on the shock generator marked from 15 volts (slight shock) to 450 (danger – severe shock).

The learner gave mainly wrong answers (on purpose), and for each of these, the teacher gave him an electric shock. When the teacher refused to administer a shock, the experimenter was to give a series of orders/prods to ensure they continued.

There were four prods, and if one was not obeyed, then the experimenter (Mr. Williams) read out the next prod, and so on.

Prod 1 : Please continue. Prod 2: The experiment requires you to continue. Prod 3 : It is absolutely essential that you continue. Prod 4 : You have no other choice but to continue.

These prods were to be used in order, and begun afresh for each new attempt at defiance (Milgram, 1974, p. 21). The experimenter also had two special prods available. These could be used as required by the situation:

• Although the shocks may be painful, there is no permanent tissue damage, so please go on’ (ibid.)
• ‘Whether the learner likes it or not, you must go on until he has learned all the word pairs correctly. So please go on’ (ibid., p. 22).

65% (two-thirds) of participants (i.e., teachers) continued to the highest level of 450 volts. All the participants continued to 300 volts.

Milgram did more than one experiment – he carried out 18 variations of his study.  All he did was alter the situation (IV) to see how this affected obedience (DV).

Conclusion 

The individual explanation for the behavior of the participants would be that it was something about them as people that caused them to obey, but a more realistic explanation is that the situation they were in influenced them and caused them to behave in the way that they did.

Some aspects of the situation that may have influenced their behavior include the formality of the location, the behavior of the experimenter, and the fact that it was an experiment for which they had volunteered and been paid.

Ordinary people are likely to follow orders given by an authority figure, even to the extent of killing an innocent human being.  Obedience to authority is ingrained in us all from the way we are brought up.

People tend to obey orders from other people if they recognize their authority as morally right and/or legally based. This response to legitimate authority is learned in a variety of situations, for example in the family, school, and workplace.

Milgram summed up in the article “The Perils of Obedience” (Milgram 1974), writing:

“The legal and philosophic aspects of obedience are of enormous import, but they say very little about how most people behave in concrete situations. I set up a simple experiment at Yale University to test how much pain an ordinary citizen would inflict on another person simply because he was ordered to by an experimental scientist. Stark authority was pitted against the subjects’ [participants’] strongest moral imperatives against hurting others, and, with the subjects’ [participants’] ears ringing with the screams of the victims, authority won more often than not. The extreme willingness of adults to go to almost any lengths on the command of an authority constitutes the chief finding of the study and the fact most urgently demanding explanation.”

Milgram’s Agency Theory

Milgram (1974) explained the behavior of his participants by suggesting that people have two states of behavior when they are in a social situation:

• The autonomous state – people direct their own actions, and they take responsibility for the results of those actions.
• The agentic state – people allow others to direct their actions and then pass off the responsibility for the consequences to the person giving the orders. In other words, they act as agents for another person’s will.

Milgram suggested that two things must be in place for a person to enter the agentic state:

• The person giving the orders is perceived as being qualified to direct other people’s behavior. That is, they are seen as legitimate.
• The person being ordered about is able to believe that the authority will accept responsibility for what happens.

According to Milgram, when in this agentic state, the participant in the obedience studies “defines himself in a social situation in a manner that renders him open to regulation by a person of higher status. In this condition the individual no longer views himself as responsible for his own actions but defines himself as an instrument for carrying out the wishes of others” (Milgram, 1974, p. 134).

Agency theory says that people will obey an authority when they believe that the authority will take responsibility for the consequences of their actions. This is supported by some aspects of Milgram’s evidence.

For example, when participants were reminded that they had responsibility for their own actions, almost none of them were prepared to obey.

In contrast, many participants who were refusing to go on did so if the experimenter said that he would take responsibility.

According to Milgram (1974, p. 188):

“The behavior revealed in the experiments reported here is normal human behavior but revealed under conditions that show with particular clarity the danger to human survival inherent in our make-up.

And what is it we have seen? Not aggression, for there is no anger, vindictiveness, or hatred in those who shocked the victim….

Something far more dangerous is revealed: the capacity for man to abandon his humanity, indeed, the inevitability that he does so, as he merges his unique personality into larger institutional structures.”

Milgram Experiment Variations

The Milgram experiment was carried out many times whereby Milgram (1965) varied the basic procedure (changed the IV).  By doing this Milgram could identify which factors affected obedience (the DV).

Obedience was measured by how many participants shocked to the maximum 450 volts (65% in the original study). Stanley Milgram conducted a total of 23 variations (also called conditions or experiments) of his original obedience study:

In total, 636 participants were tested in 18 variation studies conducted between 1961 and 1962 at Yale University.

In the original baseline study – the experimenter wore a gray lab coat to symbolize his authority (a kind of uniform).

The lab coat worn by the experimenter in the original study served as a crucial symbol of scientific authority that increased obedience. The lab coat conveyed expertise and legitimacy, making participants see the experimenter as more credible and trustworthy.

Milgram carried out a variation in which the experimenter was called away because of a phone call right at the start of the procedure.

The role of the experimenter was then taken over by an ‘ordinary member of the public’ ( a confederate) in everyday clothes rather than a lab coat. The obedience level dropped to 20%.

Change of Location:  The Mountain View Facility Study (1963, unpublished)

Milgram conducted this variation in a set of offices in a rundown building, claiming it was associated with “Research Associates of Bridgeport” rather than Yale.

The lab’s ordinary appearance was designed to test if Yale’s prestige encouraged obedience. Participants were led to believe that a private research firm experimented.

In this non-university setting, obedience rates dropped to 47.5% compared to 65% in the original Yale experiments. This suggests that the status of location affects obedience.

Private research firms are viewed as less prestigious than certain universities, which affects behavior. It is easier under these conditions to abandon the belief in the experimenter’s essential decency.

The impressive university setting reinforced the experimenter’s authority and conveyed an implicit approval of the research.

Milgram filmed this variation for his documentary Obedience , but did not publish the results in his academic papers. The study only came to wider light when archival materials, including his notes, films, and data, were studied by later researchers like Perry (2013) in the decades after Milgram’s death.

Two Teacher Condition

When participants could instruct an assistant (confederate) to press the switches, 92.5% shocked to the maximum of 450 volts.

Allowing the participant to instruct an assistant to press the shock switches diffused personal responsibility and likely reduced perceptions of causing direct harm.

By attributing the actions to the assistant rather than themselves, participants could more easily justify shocking to the maximum 450 volts, reflected in the 92.5% obedience rate.

When there is less personal responsibility, obedience increases. This relates to Milgram’s Agency Theory.

Touch Proximity Condition

The teacher had to force the learner’s hand down onto a shock plate when the learner refused to participate after 150 volts. Obedience fell to 30%.

Forcing the learner’s hand onto the shock plate after 150 volts physically connected the teacher to the consequences of their actions. This direct tactile feedback increased the teacher’s personal responsibility.

No longer shielded from the learner’s reactions, the proximity enabled participants to more clearly perceive the harm they were causing, reducing obedience to 30%. Physical distance and indirect actions in the original setup made it easier to rationalize obeying the experimenter.

The participant is no longer buffered/protected from seeing the consequences of their actions.

Social Support Condition

When the two confederates set an example of defiance by refusing to continue the shocks, especially early on at 150 volts, it permitted the real participant also to resist authority.

Two other participants (confederates) were also teachers but refused to obey. Confederate 1 stopped at 150 volts, and Confederate 2 stopped at 210 volts.

Their disobedience provided social proof that it was acceptable to disobey. This modeling of defiance lowered obedience to only 10% compared to 65% without such social support. It demonstrated that social modeling can validate challenging authority.

The presence of others who are seen to disobey the authority figure reduces the level of obedience to 10%.

Absent Experimenter Condition 

It is easier to resist the orders from an authority figure if they are not close by. When the experimenter instructed and prompted the teacher by telephone from another room, obedience fell to 20.5%.

Many participants cheated and missed out on shocks or gave less voltage than ordered by the experimenter. The proximity of authority figures affects obedience.

The physical absence of the authority figure enabled participants to act more freely on their own moral inclinations rather than the experimenter’s commands. This highlighted the role of an authority’s direct presence in influencing behavior.

A key reason the obedience studies fascinate people is Milgram presented them as a scientific experiment, contrasting himself as an “empirically grounded scientist” compared to philosophers. He claimed he systematically varied factors to alter obedience rates.

However, recent scholarship using archival records shows Milgram’s account of standardizing the procedure was misleading. For example, he published a list of standardized prods the experimenter used when participants questioned continuing. Milgram said these were delivered uniformly in a firm but polite tone.

Analyzing audiotapes, Gibson (2013) found considerable variation from the published protocol – the prods differed across trials. The point is not that Milgram did poor science, but that the archival materials reveal the limitations of the textbook account of his “standardized” procedure.

The qualitative data like participant feedback, Milgram’s notes, and researchers’ actions provide a fuller, messier picture than the obedience studies’ “official” story. For psychology students, this shows how scientific reporting can polish findings in a way that strays from the less tidy reality.

Critical Evaluation

Inaccurate description of the prod methodology:.

A key reason the obedience studies fascinate people is Milgram (1974) presented them as a scientific experiment, contrasting himself as an “empirically grounded scientist” compared to philosophers. He claimed he systematically varied factors to alter obedience rates.

However, recent scholarship using archival records shows Milgram’s account of standardizing the procedure was misleading. For example, he published a list of standardized prods the experimenter used when participants questioned continuing. Milgram said these were delivered uniformly in a firm but polite tone (Gibson, 2013; Perry, 2013; Russell, 2010).

Perry’s (2013) archival research revealed another discrepancy between Milgram’s published account and the actual events. Milgram claimed standardized prods were used when participants resisted, but Perry’s audiotape analysis showed the experimenter often improvised more coercive prods beyond the supposed script.

This off-script prodding varied between experiments and participants, and was especially prevalent with female participants where no gender obedience difference was found – suggesting the improvisation influenced results. Gibson (2013) and Russell (2009) corroborated the experimenter’s departures from the supposed fixed prods. 

Prods were often combined or modified rather than used verbatim as published.

Russell speculated the improvisation aimed to achieve outcomes the experimenter believed Milgram wanted. Milgram seemed to tacitly approve of the deviations by not correcting them when observing.

This raises significant issues around experimenter bias influencing results, lack of standardization compromising validity, and ethical problems with Milgram misrepresenting procedures.

Milgram’s experiment lacked external validity:

The Milgram studies were conducted in laboratory-type conditions, and we must ask if this tells us much about real-life situations.

We obey in a variety of real-life situations that are far more subtle than instructions to give people electric shocks, and it would be interesting to see what factors operate in everyday obedience. The sort of situation Milgram investigated would be more suited to a military context.

Orne and Holland (1968) accused Milgram’s study of lacking ‘experimental realism,”’ i.e.,” participants might not have believed the experimental set-up they found themselves in and knew the learner wasn’t receiving electric shocks.

“It’s more truthful to say that only half of the people who undertook the experiment fully believed it was real, and of those two-thirds disobeyed the experimenter,” observes Perry (p. 139).

Milgram’s sample was biased:

• The participants in Milgram’s study were all male. Do the findings transfer to females?
• Milgram’s study cannot be seen as representative of the American population as his sample was self-selected. This is because they became participants only by electing to respond to a newspaper advertisement (selecting themselves).
• They may also have a typical “volunteer personality” – not all the newspaper readers responded so perhaps it takes this personality type to do so.

Yet a total of 636 participants were tested in 18 separate experiments across the New Haven area, which was seen as being reasonably representative of a typical American town.

Milgram’s findings have been replicated in a variety of cultures and most lead to the same conclusions as Milgram’s original study and in some cases see higher obedience rates.

However, Smith and Bond (1998) point out that with the exception of Jordan (Shanab & Yahya, 1978), the majority of these studies have been conducted in industrialized Western cultures, and we should be cautious before we conclude that a universal trait of social behavior has been identified.

Selective reporting of experimental findings:

Perry (2013) found Milgram omitted findings from some obedience experiments he conducted, reporting only results supporting his conclusions. A key omission was the Relationship condition (conducted in 1962 but unpublished), where participant pairs were relatives or close acquaintances.

When the learner protested being shocked, most teachers disobeyed, contradicting Milgram’s emphasis on obedience to authority.

Perry argued Milgram likely did not publish this 85% disobedience rate because it undermined his narrative and would be difficult to defend ethically since the teacher and learner knew each other closely.

Milgram’s selective reporting biased interpretations of his findings. His failure to publish all his experiments raises issues around researchers’ ethical obligation to completely and responsibly report their results, not just those fitting their expectations.

Unreported analysis of participants’ skepticism and its impact on their behavior:

Perry (2013) found archival evidence that many participants expressed doubt about the experiment’s setup, impacting their behavior. This supports Orne and Holland’s (1968) criticism that Milgram overlooked participants’ perceptions.

Incongruities like apparent danger, but an unconcerned experimenter likely cued participants that no real harm would occur. Trust in Yale’s ethics reinforced this. Yet Milgram did not publish his assistant’s analysis showing participant skepticism correlated with disobedience rates and varied by condition.

Obedient participants were more skeptical that the learner was harmed. This selective reporting biased interpretations. Additional unreported findings further challenge Milgram’s conclusions.

This highlights issues around thoroughly and responsibly reporting all results, not just those fitting expectations. It shows how archival evidence makes Milgram’s study a contentious classic with questionable methods and conclusions.

Ethical Issues

What are the potential ethical concerns associated with Milgram’s research on obedience?

While not a “contribution to psychology” in the traditional sense, Milgram’s obedience experiments sparked significant debate about the ethics of psychological research.

Baumrind (1964) criticized the ethics of Milgram’s research as participants were prevented from giving their informed consent to take part in the study. 

Participants assumed the experiment was benign and expected to be treated with dignity.

As a result of studies like Milgram’s, the APA and BPS now require researchers to give participants more information before they agree to take part in a study.

The participants actually believed they were shocking a real person and were unaware the learner was a confederate of Milgram’s.

However, Milgram argued that “illusion is used when necessary in order to set the stage for the revelation of certain difficult-to-get-at-truths.”

Milgram also interviewed participants afterward to find out the effect of the deception. Apparently, 83.7% said that they were “glad to be in the experiment,” and 1.3% said that they wished they had not been involved.

Protection of participants 

Participants were exposed to extremely stressful situations that may have the potential to cause psychological harm. Many of the participants were visibly distressed (Baumrind, 1964).

Signs of tension included trembling, sweating, stuttering, laughing nervously, biting lips and digging fingernails into palms of hands. Three participants had uncontrollable seizures, and many pleaded to be allowed to stop the experiment.

Milgram described a businessman reduced to a “twitching stuttering wreck” (1963, p. 377),

In his defense, Milgram argued that these effects were only short-term. Once the participants were debriefed (and could see the confederate was OK), their stress levels decreased.

“At no point,” Milgram (1964) stated, “were subjects exposed to danger and at no point did they run the risk of injurious effects resulting from participation” (p. 849).

To defend himself against criticisms about the ethics of his obedience research, Milgram cited follow-up survey data showing that 84% of participants said they were glad they had taken part in the study.

Milgram used this to claim that the study caused no serious or lasting harm, since most participants retrospectively did not regret their involvement.

Yet archival accounts show many participants endured lasting distress, even trauma, refuting Milgram’s insistence the study caused only fleeting “excitement.” By not debriefing all, Milgram misled participants about the true risks involved (Perry, 2013).

However, Milgram did debrief the participants fully after the experiment and also followed up after a period of time to ensure that they came to no harm.

Milgram debriefed all his participants straight after the experiment and disclosed the true nature of the experiment.

Participants were assured that their behavior was common, and Milgram also followed the sample up a year later and found no signs of any long-term psychological harm.

The majority of the participants (83.7%) said that they were pleased that they had participated, and 74% had learned something of personal importance.

Perry’s (2013) archival research found Milgram misrepresented debriefing – around 600 participants were not properly debriefed soon after the study, contrary to his claims. Many only learned no real shocks occurred when reading a mailed study report months later, which some may have not received.

Milgram likely misreported debriefing details to protect his credibility and enable future obedience research. This raises issues around properly informing and debriefing participants that connect to APA ethics codes developed partly in response to Milgram’s study.

Right to Withdrawal 

The BPS states that researchers should make it plain to participants that they are free to withdraw at any time (regardless of payment).

When expressing doubts, the experimenter assured them all was well. Trusting Yale scientists, many took the experimenter at his word that “no permanent tissue damage” would occur, and continued administering shocks despite reservations.

Did Milgram give participants an opportunity to withdraw? The experimenter gave four verbal prods which mostly discouraged withdrawal from the experiment:

• Please continue.
• The experiment requires that you continue.
• It is absolutely essential that you continue.
• You have no other choice, you must go on.

Milgram argued that they were justified as the study was about obedience, so orders were necessary.

Milgram pointed out that although the right to withdraw was made partially difficult, it was possible as 35% of participants had chosen to withdraw.

Replications

Direct replications have not been possible due to current ethical standards . However, several researchers have conducted partial replications and variations that aim to reproduce some aspects of Milgram’s methods ethically.

One important replication was conducted by Jerry Burger in 2009. Burger’s partial replication included several safeguards to protect participant welfare, such as screening out high-risk individuals, repeatedly reminding participants they could withdraw, and stopping at the 150-volt shock level. This was the point where Milgram’s participants first heard the learner’s protests.

As 79% of Milgram’s participants who went past 150 volts continued to the maximum 450 volts, Burger (2009) argued that 150 volts provided a reasonable estimate for obedience levels. He found 70% of participants continued to 150 volts, compared to 82.5% in Milgram’s comparable condition.

Another replication by Thomas Blass (1999) examined whether obedience rates had declined over time due to greater public awareness of the experiments. Blass correlated obedience rates from replication studies between 1963 and 1985 and found no relationship between year and obedience level. He concluded that obedience rates have not systematically changed, providing evidence against the idea of “enlightenment effects”.

Some variations have explored the role of gender. Milgram found equal rates of obedience for male and female participants. Reviews have found most replications also show no gender difference, with a couple of exceptions (Blass, 1999). For example, Kilham and Mann (1974) found lower obedience in female participants.

Partial replications have also examined situational factors. Having another person model defiance reduced obedience compared to a solo participant in one study, but did not eliminate it (Burger, 2009). The authority figure’s perceived expertise seems to be an influential factor (Blass, 1999). Replications have supported Milgram’s observation that stepwise increases in demands promote obedience.

Personality factors have been studied as well. Traits like high empathy and desire for control correlate with some minor early hesitation, but do not greatly impact eventual obedience levels (Burger, 2009). Authoritarian tendencies may contribute to obedience (Elms, 2009).

In sum, the partial replications confirm Milgram’s degree of obedience. Though ethical constraints prevent full reproductions, the key elements of his procedure seem to consistently elicit high levels of compliance across studies, samples, and eras. The replications continue to highlight the power of situational pressures to yield obedience.

Milgram (1963) Audio Clips

Below you can also hear some of the audio clips taken from the video that was made of the experiment. Just click on the clips below.

Why was the Milgram experiment so controversial?

The Milgram experiment was controversial because it revealed people’s willingness to obey authority figures even when causing harm to others, raising ethical concerns about the psychological distress inflicted upon participants and the deception involved in the study.

Would Milgram’s experiment be allowed today?

Milgram’s experiment would likely not be allowed today in its original form, as it violates modern ethical guidelines for research involving human participants, particularly regarding informed consent, deception, and protection from psychological harm.

Did anyone refuse the Milgram experiment?

Yes, in the Milgram experiment, some participants refused to continue administering shocks, demonstrating individual variation in obedience to authority figures. In the original Milgram experiment, approximately 35% of participants refused to administer the highest shock level of 450 volts, while 65% obeyed and delivered the 450-volt shock.

How can Milgram’s study be applied to real life?

Milgram’s study can be applied to real life by demonstrating the potential for ordinary individuals to obey authority figures even when it involves causing harm, emphasizing the importance of questioning authority, ethical decision-making, and fostering critical thinking in societal contexts.

Were all participants in Milgram’s experiments male?

Yes, in the original Milgram experiment conducted in 1961, all participants were male, limiting the generalizability of the findings to women and diverse populations.

Why was the Milgram experiment unethical?

The Milgram experiment was considered unethical because participants were deceived about the true nature of the study and subjected to severe emotional distress. They believed they were causing harm to another person under the instruction of authority.

Additionally, participants were not given the right to withdraw freely and were subjected to intense pressure to continue. The psychological harm and lack of informed consent violates modern ethical guidelines for research.

Baumrind, D. (1964). Some thoughts on ethics of research: After reading Milgram’s” Behavioral study of obedience.”.  American Psychologist ,  19 (6), 421.

Blass, T. (1999). The Milgram paradigm after 35 years: Some things we now know about obedience to authority 1.  Journal of Applied Social Psychology ,  29 (5), 955-978.

Brannigan, A., Nicholson, I., & Cherry, F. (2015). Introduction to the special issue: Unplugging the Milgram machine.  Theory & Psychology ,  25 (5), 551-563.

Burger, J. M. (2009). Replicating Milgram: Would people still obey today? American Psychologist, 64 , 1–11.

Elms, A. C. (2009). Obedience lite. American Psychologist, 64 (1), 32–36.

Gibson, S. (2013). Milgram’s obedience experiments: A rhetorical analysis. British Journal of Social Psychology, 52, 290–309.

Gibson, S. (2017). Developing psychology’s archival sensibilities: Revisiting Milgram’s obedience’ experiments.  Qualitative Psychology ,  4 (1), 73.

Griggs, R. A., Blyler, J., & Jackson, S. L. (2020). Using research ethics as a springboard for teaching Milgram’s obedience study as a contentious classic.  Scholarship of Teaching and Learning in Psychology ,  6 (4), 350.

Haslam, S. A., & Reicher, S. D. (2018). A truth that does not always speak its name: How Hollander and Turowetz’s findings confirm and extend the engaged followership analysis of harm-doing in the Milgram paradigm. British Journal of Social Psychology, 57, 292–300.

Haslam, S. A., Reicher, S. D., & Birney, M. E. (2016). Questioning authority: New perspectives on Milgram’s ‘obedience’ research and its implications for intergroup relations. Current Opinion in Psychology, 11 , 6–9.

Haslam, S. A., Reicher, S. D., Birney, M. E., Millard, K., & McDonald, R. (2015). ‘Happy to have been of service’: The Yale archive as a window into the engaged followership of participants in Milgram’s ‘obedience’ experiment. British Journal of Social Psychology, 54 , 55–83.

Kaplan, D. E. (1996). The Stanley Milgram papers: A case study on appraisal of and access to confidential data files. American Archivist, 59 , 288–297.

Kaposi, D. (2022). The second wave of critical engagement with Stanley Milgram’s ‘obedience to authority’experiments: What did we learn?.  Social and Personality Psychology Compass ,  16 (6), e12667.

Kilham, W., & Mann, L. (1974). Level of destructive obedience as a function of transmitter and executant roles in the Milgram obedience paradigm. Journal of Personality and Social Psychology, 29 (5), 696–702.

Milgram, S. (1963). Behavioral study of obedience . Journal of Abnormal and Social Psychology , 67, 371-378.

Milgram, S. (1964). Issues in the study of obedience: A reply to Baumrind. American Psychologist, 19 , 848–852.

Milgram, S. (1965). Some conditions of obedience and disobedience to authority . Human Relations, 18(1) , 57-76.

Milgram, S. (1974). Obedience to authority: An experimental view . Harpercollins.

Miller, A. G. (2009). Reflections on” Replicating Milgram”(Burger, 2009), American Psychologis t, 64 (1):20-27

Nicholson, I. (2011). “Torture at Yale”: Experimental subjects, laboratory torment and the “rehabilitation” of Milgram’s “obedience to authority”. Theory & Psychology, 21 , 737–761.

Nicholson, I. (2015). The normalization of torment: Producing and managing anguish in Milgram’s “obedience” laboratory. Theory & Psychology, 25 , 639–656.

Orne, M. T., & Holland, C. H. (1968). On the ecological validity of laboratory deceptions. International Journal of Psychiatry, 6 (4), 282-293.

Orne, M. T., & Holland, C. C. (1968). Some conditions of obedience and disobedience to authority. On the ecological validity of laboratory deceptions. International Journal of Psychiatry, 6 , 282–293.

Perry, G. (2013). Behind the shock machine: The untold story of the notorious Milgram psychology experiments . New York, NY: The New Press.

Reicher, S., Haslam, A., & Miller, A. (Eds.). (2014). Milgram at 50: Exploring the enduring relevance of psychology’s most famous studies [Special issue]. Journal of Social Issues, 70 (3), 393–602

Russell, N. (2014). Stanley Milgram’s obedience to authority “relationship condition”: Some methodological and theoretical implications. Social Sciences, 3, 194–214

Shanab, M. E., & Yahya, K. A. (1978). A cross-cultural study of obedience. Bulletin of the Psychonomic Society .

Smith, P. B., & Bond, M. H. (1998). Social psychology across cultures (2nd Edition) . Prentice Hall.

Further Reading

• The power of the situation: The impact of Milgram’s obedience studies on personality and social psychology
• Seeing is believing: The role of the film Obedience in shaping perceptions of Milgram’s Obedience to Authority Experiments
• Replicating Milgram: Would people still obey today?

Learning Check

Which is true regarding the Milgram obedience study?

• The aim was to see how obedient people would be in a situation where following orders would mean causing harm to another person.
• Participants were under the impression they were part of a learning and memory experiment.
• The “learners” in the study were actual participants who volunteered to be shocked as part of the experiment.
• The “learner” was an actor who was in on the experiment and never actually received any real shocks.
• Although the participant could not see the “learner”, he was able to hear him clearly through the wall
• The study was directly influenced by Milgram’s observations of obedience patterns in post-war Europe.
• The experiment was designed to understand the psychological mechanisms behind war crimes committed during World War II.
• The Milgram study was universally accepted in the psychological community, and no ethical concerns were raised about its methodology.
• When Milgram’s experiment was repeated in a rundown office building in Bridgeport, the percentage of the participants who fully complied with the commands of the experimenter remained unchanged.
• The experimenter (authority figure) delivered verbal prods to encourage the teacher to continue, such as ‘Please continue’ or ‘Please go on’.
• Over 80% of participants went on to deliver the maximum level of shock.
• Milgram sent participants questionnaires after the study to assess the effects and found that most felt no remorse or guilt, so it was ethical.
• The aftermath of the study led to stricter ethical guidelines in psychological research.
• The study emphasized the role of situational factors over personality traits in determining obedience.

Answers : Items 3, 8, 9, and 11 are the false statements.

Short Answer Questions

• Briefly explain the results of the original Milgram experiments. What did these results prove?
• List one scenario on how an authority figure can abuse obedience principles.
• List one scenario on how an individual could use these principles to defend their fellow peers.
• In a hospital, you are very likely to obey a nurse. However, if you meet her outside the hospital, for example in a shop, you are much less likely to obey. Using your knowledge of how people resist pressure to obey, explain why you are less likely to obey the nurse outside the hospital.
• Describe the shock instructions the participant (teacher) was told to follow when the victim (learner) gave an incorrect answer.
• State the lowest voltage shock that was labeled on the shock generator.
• What would likely happen if Milgram’s experiment included a condition in which the participant (teacher) had to give a high-level electric shock for the first wrong answer?

Group Activity

Gather in groups of three or four to discuss answers to the short answer questions above.

For question 2, review the different scenarios you each came up with. Then brainstorm on how these situations could be flipped.

For question 2, discuss how an authority figure could instead empower those below them in the examples your groupmates provide.

For question 3, discuss how a peer could do harm by using the obedience principles in the scenarios your groupmates provide.

Essay Topic

• What’s the most important lesson of Milgram’s Obedience Experiments? Fully explain and defend your answer.
• Milgram selectively edited his film of the obedience experiments to emphasize obedient behavior and minimize footage of disobedience. What are the ethical implications of a researcher selectively presenting findings in a way that fits their expected conclusions?

A Solar Eclipse Means Big Science

By Katrina Miller April 1, 2024

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On April 8, cameras all over North America will make a “megamovie” of the sun’s corona, like this one from the 2017 eclipse. The time lapse will help scientists track the behavior of jets and plumes on the sun’s surface.

There’s more science happening along the path of totality →

An app named SunSketcher will help the public take pictures of the eclipse with their phones.

Scientists will use these images to study deviations in the shape of the solar surface , which will help them understand the sun’s churning behavior below.

The sun right now is approaching peak activity. More than 40 telescope stations along the eclipse’s path will record totality.

By comparing these videos to what was captured in 2017 — when the sun was at a lull — researchers can learn how the sun’s magnetism drives the solar wind, or particles that stream through the solar system.

Students will launch giant balloons equipped with cameras and sensors along the eclipse’s path.

Their measurements may improve weather forecasting , and also produce a bird’s eye view of the moon’s shadow moving across the Earth.

Ham radio operators will send signals to each other across the path of totality to study how the density of electrons in Earth’s upper atmosphere changes .

This can help quantify how space weather produced by the sun disrupts radar communication systems.

(Animation by Dr. Joseph Huba, Syntek Technologies; HamSCI Project, Dr. Nathaniel Frissell, the University of Scranton, NSF and NASA.)

NASA is also studying Earth’s atmosphere, but far from the path of totality.

In Virginia, the agency will launch rockets during the eclipse to measure how local drops in sunlight cause ripple effects hundreds of miles away . The data will clarify how eclipses and other solar events affect satellite communications, including GPS.

Biologists in San Antonio plan to stash recording devices in beehives to study how bees orient themselves using sunlight , and how the insects respond to the sudden atmospheric changes during a total eclipse.

Two researchers in southern Illinois will analyze social media posts to understand tourism patterns in remote towns , including when visitors arrive, where they come from and what they do during their visits.

Results can help bolster infrastructure to support large events in rural areas.

Read more about the eclipse:

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