Stanford Prison Experiment

The Stanford Prison Experiment


The Purpose

The Stanford prison experiment was a study of the psychological effect of becoming a prisoner or prison guard. Lasting for only six days, from August 14 to 20, 1971, the experiment was conducted by a team of researchers at Stanford University led by the psychology professor Phillip Zimbardo.

The Set-Up

In the experiment, Zimbardo and his team wanted to test the idea that abusive prison situations were caused by the inherent personality traits of prisoners and guards.Zimbardo’s team placed an ad in the local newspaper calling for volunteers in a two-week prison simulation.Out of the 75 respondents, most of whom were white and middle-class, Zimbardo and his team chose the 24 males whom they deemed to be the most psychologically stable and healthy to participate in the study. The participants were randomly divided into two groups by a coin flip, half of them assigned the roles of guards, the other half prison inmates.

The Beginning

The day before the experiment, the researchers held an orientation session for guards.During this session, the guards were told that they were not permitted to physically harm the prisoners, but they could use various psychological methods to degrade and dehumanize the prisoners in order to instill a feeling of powerlessness.On the first day of the experiment, participants assigned the role of prisoners were arrested at their homes by the local police department, which had agreed to assist Zimbardo, and charged with armed robbery. Afterwards, the prisoners were transported to a mock prison in the basement of one of the buildings at Stanford University, where they were to be given their new identities.

The Beginning (cont’d)

Upon arrival, the prisoners were each greeted individually by the warden, who recounted to them the seriousness of their crimes.Each prisoner was then strip-searched and deloused, providing a humiliating experience.Prisoners were forced to wear uncomfortable clothing and assigned numbers, sewn to their uniforms, by which guards addressed them, rather than calling them by name. A chain around their ankle further reinforced the role of prisoner.Guards were provided with wooden batons, meant to establish their status, which were not to be used on prisoners.The Guards were also outfitted in khaki pants and shirts from a military surplus store, and provided with mirrored sunglasses in order to prevent eye contact with prisoners.

The Guards

The experiment began with nine guards and nine prisoners in the jail.Three guards worked three eight hour shifts each, while each of the three cells constantly contained three prisoners.Prisoners were awakened from sleep at 2:30 AM for “counts”, serving to familiarize the prisoners with their numbers.Early on, the prisoners were still trying to assert their independence and the guards were inexperienced, leading to some confrontations between prisoners and guards.Guards began using push-ups as a form of physical punishment, and one of the guards would step on the prisoners’ backs, or make other prisoners sit or step on the backs of their inmates doing push-ups.


Though the first day of the experiment passed without incident, on the morning of the second day, a rebellion broke out.Prisoners removed their stocking caps, ripped off their numbers, and used their beds to barricade themselves inside their cells.The guards were frustrated and angry with the prisoners, especially once the inmates began to taunt and curse them, and even angry with each other; once the morning guards came in, they were angry with the night guards, who they felt must have been too lenient. In order to handle the rebellion, the guards first called in reinforcements, bringing in the three guards who were waiting at home on stand-by call.The guards then used a fire extinguisher to force the prisoners away from the doors with bursts of ice-cold CO2. reinforcements arrived, the guards broke into each cell, stripping the prisoners and removing their beds.After the rebellion, the guards began to harass and intimidate the prisoners.

Controlling the Prisoners

After the rebellion was put down, the guards had to find a way to keep the prisoners under control.Faced with the problem of an insufficient staff-to-prisoner ratio, one of the guards came up with the solution of using psychological tactics rather than physical ones to control the prisoners.One of the three cells was designates as a “privilege cell”, where the three prisoners least involved in the rebellion were given special privileges.This was attempted in order to break the solidarity among prisoners.

Controlling the Prisoners (cont’d)

The guards then took some of these privileged prisoners and put them into “bad” cells, replacing them with some of the “bad” prisoners after half a day.Some of the ringleaders now thought that the prisoners from the privileged cell must be informers for the guards, and distrust began to grow between the prisoners.The rebellion also bolstered solidarity among the guards.Instead of seeing the experiment as only a simulation, guards began to see the prisoners as troublemakers who were out to get them, and began increasing their control, surveillance and aggression accordingly.

Descending Into Tyranny

The guards began to control every single aspect of the prisoners’ lives, even the ability to be able to go to the toilet.Occasionally, guards would not allow prisoners to empty their waste buckets, adding to the degrading atmosphere of the prison.The guards were especially tough on Prisoner #5401, who had orchestrated the rebellion. Prisoner #5401 was a heavy smoker, and the guards would control him by regulating his ability to smoke. Some of the guard became increasingly cruel as the experiment continued, with experimenters saying that one-third of the guards exhibited genuine sadistic tendencies.When a visiting hour was held for parents and friends, the experimenters manipulated both the situation and the visitors by making the prison environment seem pleasant.The experimenters had the prisoners washed, shaved, and groomed, had them clean their cells, fed them, and played music on the intercom.When the visitors came, the experimenters had them register, wait half an hour, and told them that only two visitors could see any one prisoner, could only have ten minutes of visiting time, and had to be under guard supervision during the visit.The parents complained about these rules, but, surprisingly, obeyed them even so.

The First Prisoner Released

Less than 36 hours into the experiment, one of the prisoners, Prisoner #8612, began to break down. Despite this, the administrative group had fallen into their roles as prison authorities to the point where they thought he was trying to fool them into releasing him.When the primary prison consultant interviewed the prisoner, he chided him for being so weak and then gave the prisoner the offer of becoming an informant in exchange for escape from guard harassment.During the next count, Prisoner #8612 began to tell other prisoners that “You can’t leave. You can’t quit”, and then began to break down even further, to the point where the administrative group became convinced that he really was suffering and had to release him.

The Escape Plot

Afterwards, one of the guards heard prisoners talking about an escape that was planned for after visiting hours.The rumor stated that Prisoner #8612 was going to round up some friends to break in and free the prisoners.Rather than recording the rumor transmission and preparing to observe the escape, the experimenters reacted with concern over the security of the prison, holding a strategy session to plan how to stop the escape.After the meeting, the experimenters decided to put an informant in the cell that Prisoner #8612 had occupied, in order to relay information about the escape plot to the administrative group.Dr. Zimbardo then went to the Palo Alto Police Department and asked the sergeant if the prisoners could be transferred to their old jail, but when he was turned down he left angry and disgusted at the lack of cooperation.

The Escape Plot (cont’d)

A second plan was formulated; the jail was to be dismantled after visiting hours, more guards were to be called in, and the prisoners were to be chained together with bags placed over their heads and then transported to a storage room until after the break in. When the people #8612 had gathered came, Dr. Zimbardo would be sitting in the prison alone and would tell them that the experiment was over and their friends had been sent home.After the conspirators left, the experimenters would bring the prisoners back and increase the security of the prison.In the end, the rumor of the prison break turned out to be just a rumor. Frustrated with the amount of wasted effort they had put into stopping the prison break, the guards noticeably increased their level of harassment, further humiliating the prisoners and forcing them to do menial, repetitive work such as cleaning out toilet bowls with their bare hands.

At this point in the study, a Catholic priest who had been a prison chaplain was invited to come and evaluate how realistic the prison situation was. The priest interviewed each prisoner individually, and half of the prisoners introduced themselves by number instead of by name.One of the prisoners, Prisoner #819, was feeling sick, had refused to eat, and wanted to see a doctor, not a priest.When he was convinced to come out of his cell and talk to the priest and superintendent he broke down and began crying hysterically.Dr. Zimbardo took the chain off his foot, the cap off his head, and told him to go rest and that he would get him some food and then take him to a doctor.While this was happening, one of the guards lined up the remaining prisoners and had them chant: “Prisoner #819 is a bad prisoner. Because of what Prisoner #819 did, my cell is a mess, Mr. Correctional Officer.”

When Dr. Zimbardo heard the chanting, he went back to the room where he had left Prisoner #819 and suggested that they leave, but the prisoner refused.He didn’t want to leave because the others had labeled him a bad prisoner, and even though he was sick, he wanted to go back and prove he was not a bad prisoner. Dr. Zimbardo had to remind him that this was just an experiment before he would agree to leave and get help.

The Guards Transform

By the fifth day, the guards fell into their jobs more easily, with three types of guards arising.There were the tough, but fair guards who followed prison rules, there were “good guys”, who did little favours for the prisoners and never punished them, and there where the hostile, arbitrary guards who were quite inventive in their forms of prisoner humiliation.These hostile guards, roughly a third of the group, appeared to enjoy the power they wielded, though none of the preliminary personality tests had predicted this type of behavior.The prisoners nicknamed the most macho and brutal guard in the study “John Wayne” because of his “Wild West” cowboy macho image in abusing the inmates.

Prisoners’ Coping styles

The prisoners coped with their feeling of powerlessness and frustration in different ways. At first, some prisoners rebelled or fought with the guards, and four prisoners reacted by breaking down emotionally. One prisoner developed a psychosomatic rash over his entire body when he learned that his parole request had been declined. Some of the prisoners tried to cope by being good prisoners, doing whatever the guards wanted them to do. By the end of the study the prisoners had fallen apart, both as individuals and as a group, with all the group unity that had been present in the beginning disintegrating as the guards gained total control of the prison.

Prisoner #416

When Prisoner #416 was admitted as one of the stand-by prisoners, unlike the other prisoners there was no gradual increasing of harassment, and he was thrown right into the worst of the study. Prisoner #416 coped by going on a hunger strike in an attempt to force his release. After the guards were unsuccessful in getting #416 to eat, they threw him into solitary confinement for 3 hours, even though rules stated that one hour was the limit. Though he should have been seen as a hero to the other prisoners, his inmates only saw him as a troublemaker. The head guard then gave the prisoners a choice; they could let #416 come out of solitary if they gave up their blankets, or they could leave him in solitary all night.Most prisoners chose to keep their blankets, and the administrative team was forced to intervene and return #416 to his cell.

The End of the Experiment

This was the point when it became clear that the study had to end.An extremely powerful situation in which prisoners were withdrawing and guards were behaving sadistically had been created, and even the “good” guards felt helpless to intervene.Dr. Zimbardo ended the study prematurely for two reasons. First, the administrators had learned that the guards were further abusing the prisoners in the middle of the night when they thought no researchers were watching. Secondly, Christina Maslach, objected to the horrible conditions of the prison. Out of around 50 outsiders, she was the only one who ever questioned its morality.


The experiment ended August 20, 1971, six days after it began. The results of the experiment have been argued to support the idea that an individual’s behaviour can be caused by a situation, rather than the individual’s personality. The experiment showed just how impressionable and obedient people can be when provided with a dehumanizing ideology and institutional support.


The experiment was heavily criticized as being unscientific and unethical. Current ethical standards of psychology would make it impossible to conduct such a study in modern times. Because the study was a field experiment, it was impossible to keep scientific controls in place, and conclusions and observations by the experimenters were very subjective. Some critics argued that participants modeled their behaviour after stereotypes, or that Zimbardo biased the guards when in his briefing he gave them clear instructions that they should oppress the prisoners.