Comparing Milgram’s Obedience and Zimbardo’s Prison Studies

This post corresponds to readings in my online textbook.on two classic social psychology studies:  Stanley Milgram’s Obedience to Authority studies and Phillip Zimbardo’s Stanford Prison Study. I wrote it to help my students better understand the similarities and differences between the two.


Original photo is here


Similarity #1. Participants in both studies had a difficult time ending their participation, and most continued all the way until the end. The reasons for this were similar in both studies.

  • By agreeing to take on the roles they had been assigned, it became very difficult for the participants to back out without breaking the implicit social rule I spoke of earlier.
  • The participants did not want to appear inconsistent by refusing to continue something they had already started.
  • The escalation in violence occurred relatively gradually, so that there was no obvious point at which they could say, “that is enough.”

Similarity #2. Both Milgram and Zimbardo stated reported the effects of personality differences were very limited. For Zimbardo, the only personality characteristic that seemed to have any effect was authoritarianism; and this characteristic was important only for prisoner behavior. Those prisoners who were high in authoritarianism were best able to handle the oppressive conditions in the prison and, thus, remained there the longest. At least four (and maybe five) of the initial group of nine prisoners, on the other hand, had to be released even before the study was ended because of severe stress caused by the conditions.

Based on results such as these, Zimbardo (1975) argued that personality differences were much less important than the social situation. In fact, Zimbardo went even farther than Milgram had by dismissing the importance of personality characteristics for most of our behaviors in everyday life:

Individual behavior is largely under the control of social forces and environmental contingencies rather than personality traits, character, will power or other empirically unvalidated constructs. Thus we create an illusion of freedom by attributing more internal control to ourselves, to the individual, than actually exists. We thus underestimate the power and pervasiveness of situational controls over behavior because: (a) they are often non-obvious and subtle, (b) we can often avoid entering situations where we might be so controlled, (c) we label as “weak” or “deviant” people in those situations who do behave differently from how we believe we would. (p. 115)

Many social psychologists took this extreme position during the 1970’s. In the next chapter (Note: this chapter does not yet appear on this site), I will discuss why they argued for this position and will try to show why it needs to be modified and softened somewhat. In fact, I would imagine that Zimbardo himself would no longer make such a strong claim, although he and many other social psychologists still give social forces a large share of the control over our behavior and mental events.


Original photo is here


Difference #1. A major difference between Zimbardo’s and Milgram’s studies is that, in the prison study, only one experimental manipulation was performed — being assigned to the role of prisoner or guard. This is a major limitation because we cannot know, as we did in the Milgram study, which factors in the situation were most important for the behaviors observed. There is no doubt that each participant’s self-definition as prisoner or guard was important, but it might have helped us to develop a deeper understanding of how such a self-definition can be maintained if Zimbardo and his colleagues had varied other factors in the situation. For example, would wearing normal clothes, which might have caused increased feelings of individuality, have resulted in decreased role-playing? Would a decrease in the reality of the simulation (perhaps by removing the bars on the doors, or having campus security “arrest” the prisoners) have done the same? It would have been very interesting, for example, if we had found that none of these factors were important — that, instead, it was simply the assigning of an arbitrary social role by an authority figure and the voluntary taking on of that role by the subject that was most important for his role-playing behavior. We probably never will be able to find out because, as I will discuss in the next section, it is unlikely that anything similar to this study could ever be performed today.

Difference #2. Milgram attempted to reduce the possibility of harming his participants as much as possible. For example, he debriefed theme as soon as the experimental session was over; and, if they demanded that the session end, he ended it. Because he believed that he had addressed many possible ethical concerns, he continued to perform experiments on obedience for several years.

Zimbardo, on the other hand, stopped his study because of ethical concerns. In fact, years later, he stated that the study was unethical as a whole. What do you think caused him to decide that the study was unethical? Probably the most important aspect of the study making it unethical was the psychological harm that was done to the prisoners. For example, most were extremely distressed by the punishments (e.g., loss of everyday privileges such as being able to go to the bathroom, eat, sleep, and so on) imposed by the guards.

Although some have argued that Milgram’s study also caused much psychological harm (e.g., Baumrind, 1965), the distress felt by the Teachers in that study was temporary (the procedure lasted only an hour), and Milgram showed that almost all had either positive or neutral feelings about the study afterwards.

Most of the participants in Zimbardo’s study, on the other hand, became very upset and, for some, this lasted for at least several months. They were brought back on several occasions after the end of the study to discuss their feelings and thoughts about the study. It’s evident from their statements that many or all of them were bothered very much by their own behavior and by the behavior of other participants.

Difference #3. Another ethical problem in Zimbardo’s study — one avoided by Milgram — was the taking on of a dual role. That is, he was both the “prison superintendent” and the principle researcher of the study. Taking on a dual role made it difficult for him to monitor the progress of the study and its effects on the participants objectively. He stopped the study only reluctantly when it was pointed out to him that the prisoners were suffering terribly. Milgram, on the other hand, was never present during the actual procedure itself, so he was able to remain more objective about any harm being done to his participants.


Baumrind, D. (1964). Some thoughts on ethics of research: After reading Milgram’s “Behavioral Study of Obedience.” American Psychologist, 19, 421-423. doi: 10.1037/h0040128
Retrieved November 24, 2011, from

Haney, C., Banks, W. C., & Zimbardo, P. G. (1973). Study of prisoners and guards in a simulated prison. Naval Research Reviews, 9, 1–17. Washington, DC: Office of Naval Research. Retrieved November 25, 2011, from

Milgram, S. (1974). Obedience to authority: An experimental view. New York: Harper & Row Publishing.

Zimbardo, P. G. (1975). On transforming experimental research into advocacy for social change. In M. Deutsch & H. Hornstein (Eds.), Applying Social Psychology: Implications For Research, Practice, and Training (pp. 33-66). Hillsdale, NJ: Lawrence Erlbaum


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