Stanford Prison Experiment

The Stanford Jail Experiment is a well-known psychological study about the influence of an extreme environment, life in prison, man-made behaviors, dependent on the social roles they developed (captive, guarded). It was carried out in 1971 by a team of researchers led by Philip Zimbardo of Stanford University . Volunteers were recruited to play the roles of guards and prisoners in a fictional prison. However, the experiment was soon gone and was canceled in the first week.

The ethical concerns surrounding famous experiments often establish comparisons with the Milgram experiment , which was carried out in 1963 at Yale University by Stanley Milgram , a former friend of Zimbardo.

Goals and methods of the experiment

The study was subsidized by the United States Navy , which sought an explanation of the conflicts in its prison system and the United States Marine Corps . Zimbardo and his team attempted to test the hypothesis that prison guards and convicts self- selected , based on a provision that would explain abuses frequently committed in prisons.

Participants were recruited through newspaper advertisements and offered a pay of $ 15 per day (equivalent to $ 88.5 per day in 2015 ) for participating in a “prison simulation”. Of the 70 candidates who responded to the announcement, Zimbardo and his team selected the 24 who considered them to be healthier and more psychologically stable. Participants were predominantly white, young, and middle-class. They were all university students.

The group of 24 youths were randomly divided into two halves: the “prisoners” and the “guards”. Later the prisoners would say that the guards had been elected for having the most robust physical build, although they were actually assigned the role by the release of a coin and there were no objective differences in stature or complexion between the two groups.

The fictional jail was installed in the basement of the Department of Psychology at Stanford University. An assistant investigator would be the “warden” and Zimbardo the “superintendent.”

Zimbardo established several specific conditions that he hoped would lead to disorientation, depersonalization, and deindividualization.

The “guards” received batons and khaki uniforms of military inspiration, which they had chosen in a military warehouse. Mirror goggles were also provided to prevent eye contact (Zimbardo said he took the idea of ​​the movie Cool Hand LukeThe Legend of the Untamed ). Unlike prisoners, guards would work in shifts and return home during off-hours, although during the experiment many volunteered to work overtime without extra pay.

The “prisoners” had to wear only muslin gowns (without underpants) and sandals with rubber heels, which Zimbardo chose to force them to adopt “unfamiliar body postures” and to contribute to their discomfort to provoke disorientation. They would be designated by numbers instead of by their names. These numbers were stitched to their uniforms. In addition, they had to wear nylon stockings on their heads to pretend they had shaved heads, much like trained recruits. In addition, they would carry a small chain around their ankles as a “constant reminder” of their imprisonment and oppression.

The day before the experiment, the guards attended a brief orientation meeting, but were given no explicit rules other than the prohibition of physical violence. They were told that it was their responsibility to run the prison, which they could do in any way they thought best.

Zimbardo transmitted the following instructions to the “guards”:

You can produce in the prisoners who feel boredom, fear to a certain extent, you can create a notion of arbitrariness and that your life is totally controlled by us, by the system, you, me, and that you will not have privacy … Let’s To strip them of their individuality in various ways. In general, all this leads to a feeling of helplessness. That is, in this situation we will have all the power and they will have none.- video The Stanford Prison Study , quoted in Haslam & Reicher, 2003.

Participants who had been selected to play the role of prisoners were simply told to wait in their homes to be “visited” on the day the experiment began. Without warning they were “charged” by theft at gunpoint and arrested by policemen actual department Palo Alto , cooperating in this part of the experiment.

The prisoners underwent a complete police detention procedure, including fingerprinting , that they will be photographed to be signed and read their Miranda rights . After this process they were transferred to the fictional prison, where they were inspected naked, ” delinquent ” and given their new identities.


The experiment was rapidly out of control. The prisoners suffered – and accepted – a sadistic and humiliating treatment at the hands of the guards, and in the end many showed serious emotional upheavals.

After a relatively dull first day, on the second day a riot broke out. The guards volunteered to do overtime and dissolve the revolt, attacking the prisoners with fire extinguishers without the direct supervision of the investigative team. From that moment, the guards tried to divide the prisoners and confront them by placing them in blocks of “good” and “bad” cells, to make them believe that there were “informants” among them. This trick was very effective, because there were no rebellions on a large scale. According to Zimbardo’s counselors, this tactic had also been used successfully in real American prisons.

The “counts” of prisoners, initially devised to help prisoners familiarize themselves with their identification numbers, evolved into traumatic experiences in which guards tortured prisoners and imposed physical punishments that included forced drills.

Hygiene and hospitality were quickly abandoned. The right to go to the lavatory became a privilege that could, as often happened, be denied. Some prisoners were forced to clean their toilets with their bare hands. The mattresses were removed from the “bad” cells and the prisoners were also forced to sleep naked on the concrete floor. Food was also often denied as a measure of punishment. They were also forced to go naked as humiliation.

Zimbardo himself has cited his own growing involvement in the experiment, which led, and in which he actively participated. On the fourth day, he and the guards reacted to the rumor of a flight plan trying to move the experiment to a block of real cells in the local police department because it was more “safe.” The police rejected his request, citing concerns for the safe and Zimbardo recalls being angry and disgusted by the lack of cooperation of the police.

As the experiment evolved, many of the guards increased their sadism, particularly at night, when they thought the cameras were off. Researchers saw about one-third of the guards showing “genuine” sadistic tendencies. Many of the guards were angry when the experiment was canceled.

One argument that Zimbardo used to support his thesis that the participants had internalized their roles was that when they were offered “parole” in exchange for all their pay, most of the prisoners accepted the deal. But when his probation was “rejected,” no one left the experiment. Zimbardo states that they had no reason to continue participating if they were able to refuse their material compensation to leave the prison.

The prisoners began to show acute emotional disorders. A prisoner developed a psychosomatic rash throughout his body upon learning that his “parole” had been rejected (Zimbardo rejected it because he thought it was a ruse to get him out of prison). Weeping and disorganized thinking became common among the prisoners. Two of them suffered traumas so severe that they were removed from the experiment and replaced.

One of the replacement prisoners, the prisoner number 416, was horrified by the treatment of the guards and went on a hunger strike . He was held in solitary confinement in a small compartment for three hours in which he was forced to hold the sausages he had refused to eat. The rest of the prisoners saw him as a troublemaker seeking trouble. To exploit this aspect, the guards offered two options: they could either hand over their blankets or leave prisoner number 416 in solitary confinement all night long. The prisoners chose to keep their blankets. Zimbardo then intervened to have 416 returned to his cell.

Zimbardo decided to end the experiment prematurely when Christina Maslach , a graduate student unfamiliar with the experiment, objected that the “prison” was showing poor conditions after being introduced for interviews. Zimbardo realized that of the more than fifty people outside the experiment who had seen the prison, she was the only one who questioned his morality. After just six days, eight ahead of schedule, the experiment was canceled.


It has been said that the result of the experiment demonstrates the impressionability and obedience of the people when they are provided with a legitimizing ideology and institutional support. It has also been used to illustrate the theory of cognitive dissonance and the power of authority .

In psychology it is often said that the result of the experiment supports theories of situational attribution of behavior to the detriment of dispositional attribution . In other words, it is assumed that it was the situation that provoked the behavior of the participants and not their individual personalities. In this way it would be compatible with the results of Milgram ‘s also famous experiment , in which ordinary people are given orders to administer what appear to be fatal electrical shocks to a fellow experimenter.

Coincidentally shortly after the completion of the study bloody riots took place in the San Quentin and Attica prisons, and Zimbardo communicated his findings to the United States Judicial Committee .

Criticism of the experiment

The experiment was widely criticized for its lack of ethics and considered within the limits of the scientific method . Critics include Erich Fromm , who questioned whether the results of the experiment could be generalized.

As it was a field work , it was impossible to carry out the traditional scientific controls. Zimbardo was not a mere neutral observer , but he controlled the direction of the experiment as “superintendent.” The conclusions and observations of the investigators were very subjective and based on anecdotes , and the experiment is very difficult to reproduce by other researchers.

Some critics of the experiment argue that participants based their behavior on how they were expected to behave or modeled on stereotypes they already had about prisoners and guards. In other words, the participants performed a mere role play . In response, Zimbardo stated that, even though it may initially have been a role-play, participants internalized their roles as the experiment continued.

The experiment was also criticized for its ecological validity . Many of the conditions imposed on the experiment were arbitrary and may not be correlated with actual prison conditions, including the arrival of blinded “prisoners”, having them wear only gowns, not allowing them to wear undergarments, preventing them from looking through Of windows and to forbid them to use their real names. Zimbardo defended himself from these criticisms by stating that imprisonment is a confusing and dehumanizing experience, and that it was necessary to encourage these procedures to give the “prisoners” proper mental conditions; But it is difficult to know how similar these effects are to those of a real prison, and the conditions of the experiment are difficult to reproduce exactly so that other researchers can draw conclusions in this regard.

Some say the study was too deterministic . The reports described significant differences in the cruelty of the guards, the worst of which was called “John Wayne” by the prisoners, but others were kinder and often granted favors to the prisoners. Zimbardo made no attempt to explain these differences.

Finally, the sample was very small, of only 24 participants in a relatively small period of time. And since the 24 interacted in the same group, it might be more correct to consider the sample size as 1.

Haslam and Reicher (2003), psychologists at the University of Exeter and the University of St. Andrews , carried out a partial replay of the experiment with the assistance of the BBC , which televised studio scenes on a reality show called ” The Experiment ” . The results and conclusions were very different from those of Zimbardo. Although his procedure was not a direct retort of Zimbardo, his study casts new doubts on the generality of his conclusions. 1

Popular culture

  • A 1999 novel by German author Mario Giordano entitled Black Box was inspired by the Stanford experiment.
  • In 2001 the BBC made a documentary, The Experiment , which recreated the experiment with volunteers. He was stopped by concerns about the well-being of the participants. 2
  • Das Experiment ( The Experiment ), a German film director Oliver Hirschbiegel shot in 2001 , is based on the novel by Mario Giordano , who in turn was inspired by this experiment.
  • The Black Box , adapted from Das Experiment , was directed by Anthony S. Beukas. It was attended by members of the Yeshiva College Dramatics Society of Yeshiva University in December 2005.
  • The story of the experiment will be filmed by Christopher McQuarrie , who won an Oscar for the script of Common Suspects , from a script he wrote with Tim Talbott .
  • On October 27, 2006, Madonna ‘s producer stopped the production of a film about the experiment. 3
  • The episode My Big Fat Greek Rush Week of the television series Veronica Mars made an allusion to the experiment when several of its main characters participated in a recreation of it. In particular, there are two characters who act similarly to “Prisoner number 416” and “John Wayne”.
  • The episode Not for nothing of the series Life revolves around a reproduction of the experiment of the jail of Stanford.
  • The 2010 American film titled The Experiment , starring Adrien Brody , is a remake of Das Experiment .
  • The case investigated in the third episode of the eighth season of the series Castle happens in a University that is recreating the same experiment, when one of the inmates appears murdered outside the complex.


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