The Stanford Prison Experiment

The Stanford Prison Experiment

The Stanford prison experiment was a study of the psychological effects of becoming a prisoner or prison guard. The experiment was conducted in 1971 by a team of researchers led by Psychology Professor Philip Zimbardo at Stanford University. Twenty-four undergraduates were selected out of 70 to play the roles of both guards and prisoners and live in a mock prison in the basement of the Stanford psychology building. Roles were assigned at random. They adapted to their roles well beyond that expected, leading the guards to display to authoritarian and even draconian measures. Two of the prisoners were upset enough by the process to quit the experiment early, and the entire experiment was abruptly stopped after only six days. The experimental process and the results remain controversial. The entire experiment was filmed, with excerpts soon made publicly available, leaving some disturbed by the resulting film. Over 30 years later, Zimbardo found renewed interest in the experiment when the Abu Ghraib torture and prisoner abuse scandal occurred.

Goals and methods

Zimbardo and his team set out to test the idea that the inherent personality traits of prisoners and guards were summarily key to understanding abusive prison situations. Participants were recruited and told they would participate in a two-week “prison simulation.” Of the 70 respondents, Zimbardo and his team selected the 24 males whom they deemed to be the most psychologically stable and healthy. These participants were predominantly white and middle-class.

The “prison” itself was in the basement of Stanford’s Jordan Hall, which had been converted into a mock jail. An undergraduate research assistant was the “warden” and Zimbardo the “superintendent”. Zimbardo set up a number of specific conditions on the participants which he hoped would promote disorientation, depersonalisation and deindividualisation.

The researchers provided weapons—wooden batons — and clothing that simulated that of a prison guard—khaki shirt and pants from a local military surplus store. They were also given mirrored sunglasses to prevent eye contact.

Prisoners wore ill-fitting smocks and stocking caps, rendering them constantly uncomfortable. Guards called prisoners by their assigned numbers, sewn on their uniforms, instead of by name. A chain around their ankles reminded them of their roles as prisoners.

The researchers held an “orientation” session for guards the day before the experiment, during which they were told that they could not physically harm the prisoners. In The Stanford Prison Study video, quoted in Haslam & Reicher, 2003, Zimbardo is seen telling the guards, “You can create in the prisoners feelings of boredom, a sense of fear to some degree, you can create a notion of arbitrariness that their life is totally controlled by us, by the system, you, me, and they’ll have no privacy… We’re going to take away their individuality in various ways. In general what all this leads to is a sense of powerlessness. That is, in this situation we’ll have all the power and they’ll have none.”

The participants chosen to play the part of prisoners were “arrested” at their homes and “charged” with armed robbery. The local Palo Alto police department assisted Zimbardo with the arrests and conducted full booking procedures on the prisoners, which included fingerprinting and taking mug shots. At the prison, they were transported to the mock prison where they were strip-searched and given their new identities.

The experiment quickly grew out of hand. Prisoners suffered — and accepted — sadistic and humiliating treatment from the guards. The high level of stress progressively led them from rebellion to inhibition. By the experiment’s end, many showed severe emotional disturbances.

After a relatively uneventful first day, a riot broke out on the second day. The guards volunteered to work extra hours and worked together to break the prisoner revolt, attacking the prisoners with fire extinguishers without supervision from the research staff.

After only 36 hours, one prisoner began to act “crazy”, Philip Zimbardo says; #8612 then began to act “crazy,” to scream, to curse, to go into a rage that seemed out of control. It took quite a while before we became convinced that he was really suffering and that we had to release him.

A false rumor spread that #8612, who was now out of the experiment, would lead companions to free the rest of the prisoners. The guards dismantled the prison and moved the inmates to another secure location. When no breakout attempt occurred, the guards were angry about having to rebuild the prison, so they took it out on the prisoners.

Guards forced the prisoners to count off repeatedly as a way to learn their prison numbers, and to reinforce the idea that this was their new identity. Guards soon used these prisoner counts as another method to harass the prisoners, using physical punishment such as protracted exercise for errors in the prisoner count. Sanitary conditions declined rapidly, made worse by the guards refusing to allow some prisoners to urinate or defecate. As punishment, the guards would not let the prisoners empty the sanitation bucket. Mattresses were a valued item in the spartan prison, so the guards would punish prisoners by removing their mattresses, leaving them to sleep on concrete. Some prisoners were forced to go nude as a method of degradation, and some were subjected to sexual humiliation, including simulated sodomy.

Zimbardo cited his own absorption in the experiment he guided, and in which he actively participated as Prison Superintendent. On the fourth day, some prisoners were talking about trying to escape. Zimbardo and the guards attempted to move the prisoners to the more secure local police station, but officials there said they could no longer participate in Zimbardo’s experiment.

Several guards became increasingly cruel as the experiment continued. Experimenters said that approximately one-third of the guards exhibited genuine sadistic tendencies. Most of the guards were upset when the experiment concluded early.

Zimbardo argued that the prisoner participants had internalized their roles, based on the fact that some had stated that they would accept parole even with the attached condition of forfeiting all of their experiment-participation pay. Yet, when their parole applications were all denied, none of the prisoner participants quit the experiment. Zimbardo argued they had no reason for continued participation in the experiment after having lost all monetary compensation, yet they did, because they had internalized the prisoner identity, they thought themselves prisoners, hence, they stayed.

Prisoner No. 416, a newly admitted stand-by prisoner, expressed concern over the treatment of the other prisoners. The guards responded with more abuse. When he refused to eat his sausages, saying he was on a hunger strike, guards confined him in a closet and called it solitary confinement. The guards used this incident to turn the other prisoners against No. 416, saying the only way he would be released from solitary confinement was if they gave up their blankets and slept on their bare mattresses, which all but one refused to do.

Zimbardo concluded the experiment early when Christina Maslach, a graduate student he was then dating (and later married), objected to the appalling conditions of the prison after she was introduced to the experiment to conduct interviews. Zimbardo noted that of more than fifty outside persons who had seen the prison, Maslach was the only one who questioned its morality. After only six days of a planned two weeks’ duration, the Stanford Prison experiment was shut down.


The Stanford experiment ended on August 20, 1971, only six days after it began instead of the fourteen it was supposed to have lasted. The experiment’s result has been argued to demonstrate the impressionability and obedience of people when provided with a legitimizing ideology and social and institutional support. It is also used to illustrate cognitive dissonance theory and the power of authority.

The results of the experiment are said to support situational attribution of behaviour rather than dispositional attribution. In other words, it seemed the situation caused the participants’ behaviour, rather than anything inherent in their individual personalities. In this way, it is compatible with the results of the also-famous Milgram experiment, in which ordinary people fulfilled orders to administer what appeared to be damaging electric shocks to a confederate of the experimenter.

Shortly after the study had been completed, there were bloody revolts at both the San Quentin and Attica prison facilities, and Zimbardo reported his findings on the experiment to the U.S. House Committee on the Judiciary.

[ Source: Wikipedia, The Stanford Prison Experiment: ]

WARNING: The following videos contain explicit images.



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