This page offers brief answers to some of the most frequently asked questions about the Stanford Prison Experiment:



Q:  What was the purpose of the Stanford Prison Experiment?

A:  The purpose was to understand the development of norms and the effects of roles, labels, and social expectations in a simulated  prison environment.

Q:  Who funded the experiment?

A:  The study was funded by a government grant from the U.S. Office of Naval Research to study antisocial behavior.

Q:  How were participants recruited?

A:  The research team placed newspaper advertisements in the Palo Alto Times and The Stanford Daily offering $15/day to male college students for a study on the psychology of imprisonment.

Q:  What were students told before the study began?

A:  Students were told that they would be assigned to play the role of prisoner or guard in a study of prison life, that they would observed and filmed, and that they would be expected to participate for the full duration of the study (see Description of Study Given to Applicants).

Q:  Who participated in the experiment?

A:   From more than 75 people who responded to the ad, 24 students were chosen: 12 to role play prisoners (9 plus 3 alternates) and 12 to role play guards (also 9 plus 3 alternates). These students had no prior record of criminal arrests, medical conditions, or psychological disorders.

Q:  How were students assigned to the role of prisoner or guard?

A:  The assignment was done randomly, as with the toss of a coin, to make sure that the prisoners and guards were comparable to each other at the beginning of the experiment.

Q:  Did participants live in the prison 24 hours per day?

A:  Prisoners remained in the prison throughout the day and night, but guards generally rotated in three 8-hour shifts. Thus, there were typically three students guarding nine prisoners.

Q:  What were the main results?

A:  There were many results, but perhaps the most important was simply this: The simulation became so real, and the guards became so abusive, that the experiment had to be shut down after only 6 days rather than the two weeks planned.

Q:  How does the movie differ from the actual Stanford Prison Experiment?

A:  Although the Stanford Prison Experiment movie was inspired by the classic 1971 experiment, there are key differences between the two. In the actual experiment, guards and prisoners were prevented from carrying out acts of physical violence such as those shown in the movie. In addition, the study ended differently than the movie. In the actual study, Professor Zimbardo's former graduate student (and future wife) Christina Maslash confronted him and said that by taking on the role of prison superintendent, he had become indifferent to the suffering of his participants. He then realized that she was right and announced that he would end the experiment the next day. The movie depicts this confrontation, but to heighten the drama, Professor Zimbardo is shown returning to the experiment and observing guards sexually humiliate the prisoners, after which he immediately ends the study.



Q:  How did the prisoner arrests take place?

A:  The Palo Alto police conducted surprise arrests at the home of prisoners. Students were handcuffed, searched, read their rights, and driven in a squad car to the police station for booking and fingerprinting. The first five prisoners were charged with burglary, and the last four were charged with armed robbery.

Q:  What rules were the prisoners required to follow?

A:  The prison warden and guards drew up a list of rules that prisoners were required to follow, such as remaining silent during rest periods, eating at meal times, and keeping the prison cells clean (see Prisoner Rules).

Q:  Were prisoners allowed to quit the experiment?

A:  Yes, and some prisoners did discontinue their participation. For the most part, however, prisoners seemed to forget or misunderstand that they could leave "through established procedures," and they reinforced a sense of imprisonment by telling each other that there was no way out.

Q:  How many prisoners left the experiment early?

A:   Half the prisoners were released early due to severe emotional or cognitive reactions.



Q:  Were the guards given any special training?

A:   No. The guards were given only a brief orientation telling them to maintain law and order, avoid physical violence, and prevent prisoner escapes.

Q:  Did personality scores predict which guards were most abusive?

A:   No. The most and least abusive guards did not differ significantly in authoritarianism, Machiavellianism, or other personality measures. Abusive guard behavior appears to have been triggered by features of the situation rather than by the personality of guards.

Q:  How many guards left the experiment early?

A:   None, although one guard later said that he had considered it.



Q:  Did students give informed consent before participating?

A:  Yes, all students signed a Consent Form before participating in the study.

Q:  Was the Stanford Prison Experiment approved by an Institutional Review Board?

A:  Yes, the study was approved by the Stanford Human Subjects Review Committee, the Stanford Psychology Department, and the Group Effectiveness Branch of the Office of Naval Research. In addition, the Student Health Department was alerted to the study and prior arrangements were made for any medical care the participants might need.

Q:  Did the APA ever review the experiment's ethics?

A:  Yes. In 1973 Professor Zimbardo asked the American Psychological Association to conduct an ethics evaluation, and the APA concluded that all existing ethical guidelines had been followed.

Q:  Has Professor Zimbardo ever apologized for the suffering that occurred?

A:  Yes. In his book The Lucifer Effect, Professor Zimbardo wrote: "I was guilty of the sin of omission -- the evil of inaction -- of not providing adequate oversight and surveillance when it was required... the findings came at the expense of human suffering. I am sorry for that and to this day apologize for contributing to this inhumanity." (pp. 181, 235)



Q:  Did any of the participants suffer lasting trauma?

A:  Despite suffering extreme emotional stress during the experiment, all participants appear to have regained their baseline emotional states after the study. Extensive follow-up testing revealed no lasting trauma to participants.

Q:  After the study ended, what became of the experimenters?

A:  All went on to distinguished careers in psychology or medicine:

  • David Jaffe, an undergraduate research associate who played the role of prison warden, is now a professor of pediatrics at Washington University.
  • Curtis Banks, a graduate student researcher, became the first African American psychology professor to receive tenure at Princeton University.
  • Craig Haney, a graduate student researcher, became a psychology professor at UC--Santa Cruz and is a leading expert on prison conditions.
  • Christina Maslach, a former graduate student who helped end the study early, is now a psychology professor and vice provost at UC--Berkeley.
  • Philip Zimbardo, who served as principle investigator and prison superintendent, became APA President in 2001 and is now a professor emeritus at Stanford University.

Q:  Are materials from the experiment archived anywhere?

A:  Yes, materials from the experiment have been preserved by the Center for the History of Psychology and the Stanford University Archives.



Q:  Who designed this website?

A:  The website was originally designed by Scott Plous and Mike Lestik in 1999. The site was redesigned in 2015 by Jeff Breil, Scott Plous, and David Jensenius.

Q:  Who manages the website?

A:  The site is managed by Social Psychology Network (SPN), a nonprofit educational organization headquartered at Wesleyan University in Middletown, Connecticut.

Q:  Who funds the website?

A:  The site is funded with generous support from the National Science Foundation (grants #9950517, #0339002, #0843855, and #1456048), SPN members, and other sources. To support this website or join Social Psychology Network, please visit the SPN Membership page.