Stanford Prison Experiment

from Wikipedia, the free encyclopedia

The Stanford Prison Experiment (German: the Stanford Prison Experiment ) was a psychological experiment to research human behavior under the conditions of captivity, especially under the field conditions of real prison life . The experiment was carried out in 1971 by the American psychologists Philip Zimbardo , Craig Haney and Curtis Banks at Stanford University and stopped prematurely. The latest findings question the correct implementation and the results of the experiment. In terms of its findings as well as its methodology and the research ethics behind it, it remains a controversial case to this day.


Application and arrest

Over 70 students responded to a newspaper advertisement placed by the scientists in Palo Alto . Diagnostic interviews and a personality test selected 24 middle-class students who achieved normal, average results. They were hired for $ 15 a day. The selected students were randomly divided into two groups - guards and prisoners - by tossing coins. The prisoners had to sign documents in advance in which they waived some of their basic rights while they were in "prison".

A few days later, the prisoners were "arrested": real police officers arrested them in public for armed robbery and break-in, clarified their rights and took them to the police station. There they waited blindfolded in examination cells. From there they were transferred to the institute and, after recording their personal details, locked them in cells specially set up for this experiment.

The three cells were in the basement of the university. The original doors of the actual laboratory rooms had been replaced by specially made lattice doors. The parcel in front of it was the "prison yard" and was closed at the ends with wooden walls. The events inside were filmed through fine holes in these walls. The experiment participants were listened to through the intercom. There were no windows, but a so-called "hole". The hole was a kind of closet that was filled with files and now had a size of 62 × 62 cm and was absolutely dark when the door was closed.

Events in the "prison"

Those who were supposed to be guards were given uniforms, bats borrowed from the police, and sunglasses. The prisoners were all greeted personally by the "deputy director". Afterwards, every prisoner was deloused and given a heavy anklet; He was dressed in a short hospital shirt without underwear and a tight-fitting cap over his hair.

The prisoners were given numbers to use in place of their names. These numbers were also written on the front and back of their smocks. In the event of an outbreak , the guards were informed that the experiment would be stopped. According to the official set-up of the experiment, the guards were free to work out rules on their own and take all necessary measures to maintain peace and order in the "prison". However, some study participants later stated that they had been urged by the study director to certain, particularly strict behavior.

The three prisoners were always locked in a cell. The cells were only big enough to fit three simple bunk beds. There were no toilets in the cells. If a prisoner had to use the bathroom, he had to get permission from a guard first. He was then blindfolded to the bathroom so that he could not see the exit.

At first, both parties tried out their roles to see where their limits were. The guards called prisoners out of bed to roll calls at any time of the day or night. On the one hand, this was intended to familiarize the prisoners with their numbers and, on the other hand, to demonstrate the absolute power of the guards over the prisoners. The guards also used push-ups as a punishment.

On the morning of the second day a riot broke out. The prisoners blocked the cell doors, tore their numbers from their smocks, and pulled their stockings off. The guards put down the riot by using fire extinguishers to spray icy carbon dioxide into the cells, forcing the prisoners to open the doors. Afterwards, all prisoners were stripped of their clothes and beds. From then on, the guards humiliated the prisoners at every opportunity and everything became a privilege. For example, after the tattoo at 10:00 pm, when the lights were off and the cells were closed , the prisoners had to use the buckets in the cells for their faeces, as the guards would not allow them to use the toilet. As a result, the prison smelled strongly of feces and urine after a short time, which further influenced the atmosphere in the stuffy vaulted cellar.

A "privileged cell" was set up for those prisoners who had not or hardly participated in the uprising. They got their clothes and beds back and also got food in the presence of the others, while they got nothing. After half a day, the privileged prisoners were mixed with the sanctioned prisoners. This caused confusion and the ringleaders of the uprising mistook the privileged for spies. In doing so, the guards broke solidarity among the prisoners and prevented further coordinated actions by the prisoners.

Escalation and termination of the experiment

The experiment quickly got out of hand. After three days, one “prisoner” showed extreme stress reactions and had to be released. Some of the guards displayed sadistic behaviors, especially at night, when they suspected the attached cameras were not operating. Sometimes the experimenters had to intervene to prevent mistreatment. After only six days (two weeks were originally planned), the experiment had to be stopped, especially because the investigators discovered that they themselves had lost their objectivity , were drawn into the experiment and acted against the prisoners' uprising.

At the end of the experiment, four prisoners had suffered emotional breakdowns and had to be released early from prison as a result. Another detainee developed a mental rash when he learned that his " parole request" had been denied. The rest of the prisoners tried to cope with the situation through submission and obey the guards' orders as correctly as possible. The group of prisoners was broken up, each one was only an individual - left to his own devices and fixated on survival.

The experiment was terminated prematurely on August 20, 1971. A meeting with all those involved one year later showed that none of those involved had any psychological long-term effects .

Psychological theories and analyzes

Guards and prisoners wore uniforms to match their roles, prisoners were given numbers to address, and guards were given mirrored sunglasses that prevented direct eye contact. The leader of the experiment gave few instructions to the participants and few restrictions were placed on their behavior. A compilation of behaviors that were remarkably similar to those in real prisons quickly developed - these included cruelty, inhuman treatment and massive disregard for fellow human beings, which were apparently present in all participants.

Zimbardo justified these behaviors with strong social forces that had to be at work here. Literally, he means (p. 208): "A number of factors have flowed into the situational forces, none of which were particularly dramatic in themselves, but which together formed a powerful synthesis." These factors are:

  • Anonymity and deindividuation
  • Power of rules and regulations
  • Roles and Responsibilities for Violations
  • Cognitive dissonance
  • Need for social approval

Anonymity and deindividuation

Among other things, by de-individualizing the participants - reducing people to their assigned roles - these behaviors were caused. Deindividuation can result from the aspects mentioned above, such as wearing the same uniform, reflective sunglasses and numbers in place of names, which makes people step back from their role, promotes anonymity and reduces personal responsibility. He “becomes” his role. The situation itself may have led to these occurrences much more than the personal characteristics of the participants.

Power of rules and regulations

Rules are a simple means of controlling human behavior. They determine what is acceptable and rewarded and what is unacceptable and therefore punished. The guards were able to justify most of the abuse of the inmates by referring to "the rules."

Roles and Responsibilities for Violations

People can easily slip into a role and internalize it quickly. This explains why the prisoners did not get the idea of ​​leaving the prison without paying, although it would have been possible if they had expressed their will. They had already internalized the role.

On the other hand, we can just as easily get rid of it and, if necessary, “explain away” our personal responsibility for the damage caused by our role-controlled behavior. The guards do not blame themselves for their transgressions, but rather their roles.

Cognitive dissonance

Cognitive dissonance is likely an important reason for internalizing role behavior and for supporting the cognitive and affective responses that have made the guards' increasingly brutal and abusive behavior.

Need for social approval

In addition to the effects of dissonance, the guards were also exposed to pressures to conform . Due to the peer pressure of the guards, it was important to be a team player and not to sit idly by watching the exceedances.


Just a few years later, criticism of the methodology of the Stanford Prison Experiment began, which continues to this day. The criticism was linked to the central methodological debate in social psychology .

Acting out stereotypes of prisoners and guards

Ali Banuzizi and Siamak Movahedi criticized the fact that the test subjects in the experiment did not react to the situations produced by the simulated prison, but rather lived out their idea of ​​how guards and prisoners behave “typically” in a prison. In the experiment, a real prison was not created, but only the appearance of a prison was created, in which the participants then only tried to behave according to the stereotypes of guards and prisoners. On the other hand, the theatricality arose from the realization that the supposed student job was actually a prison-like situation when participants willing to drop out found out that they could not leave the simulation prematurely.

Reproducibility of the experiment

There were doubts about the generalizability of the results of the experiment. In contrast to the Milgram experiment , in which the experiment was carried out in different variants in a thousand processes, the Stanford Prison experiment consisted of a total of only one process lasting several days. In one case, the experiment was reproduced in Australia with similar results, but in another reproduction for the BBC , the conflict did not escalate, but rather solidarity between guards and prisoners.

Influence of the result by the experimenter

Methodologically, it is particularly criticized that the test supervisor Philip Zimbardo , who is actually obliged to neutrality and objectivity, was also active as a senior enforcement officer in the role play and was able to influence the guards under him on an ongoing basis in the sense of the result he expected. In retrospect, various participants stated that they only acted on their behavior because they were encouraged to do so or because they wanted to meet expectations. It was later referred to as "targeted improv theater" by various participants in the experiment. The social scientist Thibault Le Texier criticizes in his book Histoire d'un mensonge that on tapes of the experiment one can hear how Zimbardo encourages the guards to behave hard.


The film Das Experiment (Germany 2001, director: Oliver Hirschbiegel , main role: Moritz Bleibtreu ) is based on the novel Black Box by Mario Giordano , which is based on the story of the Stanford Prison Experiment. The film "advertised" with the subtitle "based on a true story". However, he portrayed the Guardians as largely sadistically motivated, which does not reflect the reality of the experiment; Only a third of the guards there showed openly sadistic behavior, while the rest of the guards set strict rules but did not affect the dignity of the prisoners. In addition, no person was killed in the experiment - unlike in the film. Under threat of legal action, Zimbardos enforced that the subtitle would not be continued.

For the German Pavilion at the Biennale in Venice , the Polish artist repeated Artur Zmijewski , the experiment in 2005 in Warsaw and documented it on film, entitled Repetition .

In August 2010 a US remake of the German film with Adrien Brody and Forest Whitaker in the leading roles was released under the title The Experiment and directed by Paul Scheuring .

In 2015, director Kyle Patrick Alvarez made another film, which had its world premiere at the 2015 Sundance Film Festival under the title The Stanford Prison Experiment and received the Alfred P. Sloan Feature Film Prize and the Waldo Salt Screenwriting Award.

See also


  • Christoph Schneider: Offenders without characteristics? On the scope of social-psychological models in Holocaust research. , in: Mittelweg 36th Journal of the Hamburg Institute for Social Research, 2011 (20) 5, pp. 3–23.
  • Michael Walter : About power structures from which crime arises. Conclusions from the Stanford prison experiment for criminology and criminal policy , in: Frank Neubacher , Michael Walter (ed.): Social psychological experiments in criminology. Milgram, Zimbardo and Rosenhan interpreted criminologically, with a sideways glance at Dürrenmatt , Lit Verlag, Münster [u. a.] 2002, ISBN 3-8258-6029-9 , pp. 93-102.
  • Philip Zimbardo : The Stanford Prison Experiment. A simulation study of the social psychology of imprisonment. 3. Edition. Santiago Verlag, Goch 2005, ISBN 3-9806468-1-5 .
  • Philip Zimbardo: The Lucifer Effect. The power of circumstances and the psychology of evil . Spectrum Akademischer Verlag, Heidelberg 2008, ISBN 978-3-8274-1990-3 .
  • Craig Haney; Curtis Banks; Philip G. Zimbardo: "Interpersonal Dynamics in a Simulated Prison", in: International Journal of Criminology and Penology 1 (1973), pp. 69-97.

Web links


  1. Banuazizi, Ali; Movahedi, Siamak, "Interpersonal Dynamics in a Simulated Prison: A Methodological Analysis," in: American Psychologist 30 (1975), pp. 152-160; see. Schneider, Christoph: “Offenders without characteristics? On the Scope of Social Psychological Models in Holocaust Research ”, in: Mittelweg 36th Journal of the Hamburg Institute for Social Research (20) 2011, pp. 3–23.
  2. "Clay Ramsay, was so dismayed on discovering that he was trapped that he started a hunger strike." -
  3. Lovibond, SH; Mithiran; Adams, WG, "The Effects of Three Experimental Prison Environments on the Behavior of Non-Convict Volunteer Subjects", in: Australian Psychologist 14 (1979), pp. 273-287.
  4. Peter Gray: Why Zimbardo's Prison Experiment Isn't in My Textbook ,, October 19, 2013, accessed January 20, 2014
  5. Sebastian Herrmann: The most important prison experiment is suspected of fraud. In: . July 9, 2018, accessed October 13, 2018 .
  6. © Stanford University, Stanford, California 94305: Tape E: 8612. Retrieved January 3, 2020 .
  7. Zimbardo, Philip G .: Stanford Prison Experiment, audio transcript - tape E. Stanford University, accessed on January 1, 2020 : “You know we're trying to set up the stereotype guard, [...] but so far your individual style has been a little too soft [...]. [Page 8]"
  8. Stanford Prison Experiment: Evil! Angry? In: ZEIT ONLINE . ( [accessed on July 15, 2018]).
  9. ^ Thibault Le Texier: Debunking the Stanford Prison Experiment. In: American Psychologist . tape 74 , no. October 7 , 2019, ISSN  1935-990X , p. 823-839 , doi : 10.1037 / amp0000401 ( [accessed January 3, 2020]).
  10. IFC Grabs Intense Sundance Winner 'The Stanford Prison Experiment'