The Stanford Prison Experiment by Philip Zimbardo

Various psychological experiments are far from uncommon. Many scientists conduct them with the aim of even more thoroughly studying the characteristics of the human psyche, his behavior, and motives for actions. And one of the most sensational experiments in its time is the Stanford prison experiment conducted in 1971 by American psychologist Philip Zimbardo. The purpose of his experiment was to study people’s reactions to the restriction of their freedom and the conditions of prison life, as well as to determine the impact that an imposed social role has on a person’s behavior.

History of the Stanford experiment

The Stanford prison experiment was designed by Zimbardo based on a similar dormitory experiment conducted by his student D. Jaffee. In F. Zimbardo's project, this student was assigned the role of assistant and outside observer.

The Stanford experiment was planned and carried out in August 1971 at the university. The scientist published an advertisement in the university newspaper that male students were invited to participate in a study on the psychology of prisoners. It was also said there that the subjects would be paid for participation in Philip Zimbardo’s prison experiment, and the experiment itself would last 2 weeks.

According to the author, students had to try themselves in two types of roles: prisoners and prison guards. This was necessary in order to track changes in human behavior in an artificially created situation.

The experiment was commissioned by the US Navy because the Navy leadership was interested in the causes of frequent conflict situations in the Marine Corps and in penal colonies.

During the experiment, D. Jaffee made notes, the analysis of which allows us to say with confidence that he himself partially shaped the cruelty in the behavior of the guards, suggesting scenarios and behavior patterns to the subjects of this group. Audio recordings confirm that Jaffee insisted on the display of cruelty and aggression on the part of the pseudo-prison guards, assuring the subjects that it was necessary for science.

Today, the experiment at Stanford University has become world famous. The goals of the experiment and its results did not coincide: during the experiment, the psychology of the subjects changed greatly. The results of the experiment shocked not only the participants, but also the initiators of this study.

Three films have been made based on Philip Zimbardo's Stanford prison experiment. There is also a book describing in detail the conduct of the Stanford Prison Experiment.

Prison conditions

“Prisoners” received three meals a day, could visit the toilet three times a day under the supervision of a jailer, and were allocated two hours for writing letters or reading. Two visits per week were allowed, and the right to exercise and watch films was also granted.

The “roll call” initially aimed to make sure that all “prisoners” were present and to test their knowledge of their numbers and rules. The first roll calls lasted about 10 minutes, but each day their duration increased, and in the end some of them lasted several hours. The “guards” changed or completely canceled many items of the daily routine that had been previously established. In addition, during the experiment, some privileges were simply forgotten by the staff.

The prison quickly became dark and dirty. The right to wash had become a privilege, and it was often denied. In addition, some “prisoners” were even forced to clean toilets with their bare hands. The mattresses were removed from the “bad” cell, and the prisoners were forced to sleep on the concrete floor. Food was often withheld as punishment.

The first day was relatively calm, but already on the second a riot broke out. To suppress it, the “guards” volunteered to work overtime. They attacked the “prisoners” with fire extinguishers. After this incident, the “jailers” tried to pit the “prisoners” against each other, to separate them, to make them think that there were “informants” among them. This had an effect, and no such major disturbances occurred in the future.

Stages of research preparation

Philip Zimbardo's experiment was carried out in several stages.

Selection of experiment participants

After an advertisement was published in the university newspaper, 70 students volunteered to take part in the Stanford Prison Experiment. All of them underwent numerous psychological examinations, based on the results of which Zimbardo selected 24 students to participate in the Stanford experiment. They had no deviations in physical and mental development.

Distribution between guards and prisoners

A feature of Philip Zimbardo’s experiment was that the subjects who were offered different roles were approximately the same age and had the same social status. They were all college students. The scientist suggested that their stock of social knowledge and baggage of life experience is approximately the same.

In real life, the students were equal to each other; the distribution into two groups was carried out randomly. However, those who were given the role of guards were told that this role went to them because they possessed the personal qualities necessary to control the behavior of prisoners. They did not undergo any special training. The day before the start of the experiment, they were invited to a briefing, where they were warned about the inadmissibility of physical violence against prisoners. They were given guard uniforms, mirrored sunglasses and batons. According to the author's plan, they were supposed to go around the prison.

Interesting Facts

Soon after the experiment, bloody riots broke out in several American prisons. On this occasion, Zimbardo contacted the authorities and advised them to apply in prisons the developments that he had arrived at through his experiment.

When a huge scandal broke out at the American prison in Iraq, Abu Ghraib, in 2004, many experts noted its similarities to the Zimbardo experiment. Among these experts was the researcher himself. He was also present at the trial of the guards. Zimbardo argued that it was wrong to place all the blame on a few “unloved” guards, since the true cause of the incident lay in the penal system itself.

In 2021, some researchers discovered that the Stanford experiment may have been staged. French sociologist Thibaut Le Texier discovered strange research notes in the Stanford University archives. Another researcher published an article disproving the results of the Stanford experiment.

Cases of acting by participants were identified, in particular, during interviews with them some time after the experiment.


In addition, it was stated above that Zimbardo himself instructed the guards how to behave before the study began, and they therefore simply played their assigned roles.

If the experiment is staged, then there is no need to talk about its scientific value. On the other hand, in this case, like the aforementioned Milgram experiment, it demonstrates how completely normal people agree to any, even the most cruel and insane actions, if they are prompted to do so by authority.

The Stanford experiment also demonstrates that psychological research is not immune to distortions caused by subjectivity, bias, and wishful thinking. And psychology itself was sometimes accused of being “unscientific,” and attempts were made to assign it the status of “parascience”—something between real science and pseudoscience. The latter, of course, is clearly overkill. The same Milgram experiment is quite objective, and multiple repetitions showed the same results. The similar Stanford experiment turned out to be simply too theatrical - the participants knew in advance the true conditions and goals of the study.

Replacement of a participant due to a hunger strike

A participant who suffered a nervous breakdown while in solitary confinement was replaced by a student from among the reserves. Finding himself in the role of a prisoner, he immediately declared that he would not obey the established rules. He tried to initiate a new rebellion by going on a hunger strike, but those participants who were in the “game” from the very beginning did not feel strong enough to openly confront.

As a result, a new prisoner with pronounced leadership abilities, without receiving support, turned into an outcast. The guards ordered the rest of the prisoners to spread rot on this rebel. The strong emotional shock and difficult psychological situation in the pseudo-prison led to the fact that by the evening this young man’s nerves gave out: further participation in the experiment could lead to irreparable consequences.


Students in the role of security guards have completely gotten used to their new status. Most of them, having received unlimited power, demonstrated cruelty. They humiliated prisoners the most at night, believing that video surveillance did not work at that time.

Seeing that events were developing rapidly, on the third day Zimbardo offered the experiment participants, playing the role of prisoners, a deal: they could leave the project by refusing any monetary reward for participating in it. All the prisoners agreed. However, in order to comply with the release procedure, they had to write a petition for clemency, which was subject to consideration by the jury (their role was performed by final year students of the Faculty of Psychology).

Voluntary refusal to receive material compensation for participating in the experiment guaranteed the students the right to immediately leave the makeshift prison. However, they all resignedly wrote a petition for clemency and went to their cells to await the decision of the jury. A few hours later they were informed that the jury had made a negative decision on all requests for clemency. This news caused a hysterical reaction in half of the prisoners.

By the sixth day, the cruelty of the guards reached its climax: they violated all ethical principles, their actions posed a serious danger to the mental health of the prisoners. The experiment had to be stopped.

Conclusions from Zimbardo's experiment

According to F. Zimbardo, the Stanford prison experiment proved that power corrupts a person. Briefly, the following conclusions can be drawn from Zimbardo’s experiment:

  1. If you give a person unlimited power, he will definitely use this power. A tendency towards cruelty will awaken in him.
  2. If under usual conditions a person is not prone to aggression, psychological pressure and humiliation of others, this does not mean that, being in a new social role, he will not behave like a despot and tyrant.
  3. Sadistic tendencies manifest themselves in a person who has never previously been seen in inhumane acts in a short time when acquiring an appropriate social role.
  4. Feeling the strength and status advantage of another person, people quickly lose the ability to withstand psychological pressure. Creative individuals cannot accept injustice longer than passive people.

The results of the experiment were later used as visual evidence of the influence of authority and as confirmation of the theory of cognitive dissonance.

What is good

...what is bad? So, “bad” is “a conscious, intentional act committed with the purpose of harming, insulting, humiliating, dehumanizing or destroying other people who are not guilty of anything; or the use of personal power and authority of the System in order to encourage people or vendita piscina gonfiabile con scivolo to allow them to do such acts in its name. In short, “knowing what is good, doing something bad” is the definition of evil given by Philip Zimbardo in his book dedicated to the Stanford experiment, “The Lucifer Effect. Why good people turn into villains." But what kind of experiment is this?

My opinion on the Stanford experiment

The study of the nature of human cruelty at the end of the last century was the subject of research by many authors. However, the most ambitious project at the end of the last century was the pseudo-prison of F. Zimbardo.

The author managed to make a significant contribution to science; the results of his experiment found practical application not only in experimental psychology.

However, I believe that the famous psychologist was not able to apply all his skill in this experiment. He failed to maintain the position of a researcher; he became involved in a dangerous game. In addition, he saw the unacceptable behavior of a group of guards, but did not apply sanctions to them, that is, he ignored moral principles. He didn't want to interrupt the experiment. Instead of sanctions for unacceptable behavior, he gave guards more and more freedom.

Many sources mention that this project was ordered by the US Navy, but nowhere does it even briefly say whether, with the help of the results of Philip Zimbardo’s experiment, the customer was able to solve problems that were pressing for them.

The results of the experiment, in my opinion, cannot be considered absolutely indicative and reliable, since the guards did not come to such behavior on their own; they acted on the instructions of D. Jaffee, who demanded that they show cruelty.

All documents describing this prison project mention the severe psychological state of the subjects at the end of the 6th day of being in terrible conditions. However, there is no information anywhere about whether any rehabilitation work was carried out with the subjects after this?

Chronicle of events

First day

In order for the prisoners to quickly get used to it and remember their numbers, they were woken up with a whistle on the very first night and had a roll call. And if at first it lasted at most 10 minutes, then later, to demonstrate their superiority, the guards stretched it out to 3 hours.

Zimbardo admitted that watching everyone during the first 24 hours, he was upset. Because he believed that his experiment would not be successful and would soon fail. The accused sought to defend their independence and protect their rights, which is why they endangered their conceived ideas. But the guards got used to the role so well that they left no chance of capitulation, and with their punishments they were able to subjugate the will of the others.

Second day

The second day began with a riot. The criminals barricaded their cells, tore numbers off their clothes and demanded a different method of treatment. But this riot was quickly pacified. Using carbon dioxide released from fire extinguishers. The one who started the resistance action was sent to the “Pit”. And the rest were stripped naked, their things were taken away, and their beds were placed in the corridor. At the same time depriving him of food.

To prevent subsequent riot attempts, the guards resorted to psychological manipulation. They created one room with improved conditions and placed three students there. They returned their clothes, allowed them to clean themselves up, and even allowed them to eat. Those who remained in normal conditions began to feel anger towards their fellow sufferers. Because they believed that these “lucky ones” were informing or trying to please their tormentors, which is why they served their sentences much more comfortably than others.

To increase the tension level, the guards began placing everyone there one by one. Confused about who the real traitor is. This cunning maneuver helped achieve the expected results. Now no one trusted each other, accordingly, aggression was directed at the victims themselves, shifting the focus from the tyrants. Which, in contrast to the others, have become much closer to each other. The supervisory team rallied and was ready to continue in the same spirit. They came up with new tortures, for example, they introduced a ban on visiting the toilet, giving them ordinary buckets, without the right to pour the contents anywhere.

At the end of the second day, criminal No. 8612 lost control of his consciousness. He had an emotional breakdown. But Philip considered his hysteria to be a game, as an attempt to terminate the agreement and return to normal life. But when the prisoner’s condition completely deteriorated, he began to experience attacks of panic and aggression, the scientists relented and finally released him.

The third day

It's time to visit your family. The experimenters decided that when loved ones saw their relatives in this state, they would immediately take them home. And the experience will end prematurely. Therefore, they quickly put things in order, combed the prisoners’ hair, allowed them to eat, wash, and shave. And they even turned on music to make the atmosphere seem less terrible and tense.

To control the situation, the security decided to introduce a little formality and introduced rules. Parents of students had to register, and the visits themselves were supervised so that no one could say anything unnecessary.

The operation, so to speak, was successful, at least there was no scandal. But another problem arose; the researchers learned that the criminals were planning an escape. As if student number 8612 actually deceived everyone about his psychological state. And he gathered his friends, wanting to free his fellow students. Just after the visitors have left. Therefore, they decided to transfer the unfortunate subjects to a storage room on the fifth floor of the university, putting bags on their heads to disorientate them in space. And Professor Zimbardo himself will be left in his original place as evidence that the experiment is completed and all participants have left the room, returning to their normal lives.

But, to everyone’s surprise, there was no band of invaders-liberators. Instead, a colleague of the professor appeared to satisfy his curiosity. And find out what results and discoveries were achieved. And at that moment Philip realized how involved he was in this prison commotion. So much so that he lost his position as an experimenter, psychologist, professor, in the end. He was angry with his colleague, his questions, which distracted him from such an important matter. Be the warden of a prison.

Realizing that the escape plan was a dud, the guards became furious. So much effort to prevent it turned out to be pointless. Therefore, the students had to experience incredible humiliation and suffering that evening as retribution. They washed toilets with their bare hands, did countless push-ups, jumped, squatted and goose-stepped. Several people could not stand it; the torture brought them to a nervous breakdown.

Fourth day

In order to find out how real the situation and atmosphere turned out to be, the researchers invited a priest to talk to the offenders. He, in turn, made the appropriate conclusions regarding the inhumane treatment of them. And he suggested contacting relatives. So that they, in turn, hire a lawyer and protect the rights of loved ones. The clergyman talked to all the prisoners except the man number 819. He felt so terrible that he became hysterical. Zimbardo managed to bring him to his senses, reminding him that this was all a role-playing game and what was happening to him was only part of the intended game.

Fifth day

On the fifth day, a commission on issues of parole was organized. The head of this commission was the man who advised the researchers at the very beginning, sharing 17 years of experience that he acquired behind bars. An interesting fact is that it was he, who knew the “kitchen” so well from the inside and understood the torment the so-called criminals were subjected to, who fiercely defended and demanded an extension of the term.

The guys were offered to give up their fees in exchange for freedom. They, of course, agreed. But, surprisingly, after the hearing was over, they obediently went back to the cells. Although, in theory, the agreement happened and they had every right to return home. This indicates how easily a person can lose touch with reality. A failure occurs in consciousness and the person simply does not understand what knowledge to rely on and what to trust. Her will is suppressed and then she believes that another person, more powerful, knows what she is doing. She gives in to doubts about her feelings and thoughts.

Sixth day

It was decided to stop the study. In short, it is because the guards began to exceed their powers, tightening their methods of exercising power. They abused the victims at night for their own pleasure, believing that the video cameras were turned off at that time. Among other things, Philip’s girlfriend, also with a degree in psychology, intervened in the process. She managed to “bring the chosen one back to his senses” a little, explaining that he had become overplayed and had lost his professional stability. Which causes her fear, since he is completely different from the one with whom she spent so much time.

Therefore, scientists had no choice but to declare the experiment prematurely ended. They had a conversation with both the guards and the prisoners, inquiring about their well-being and general impressions. Then they were put into one group so that all participants could hear feedback. We also jointly tried to discover alternative solutions to conflict situations that arose over the course of 6 days.

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