A research group mentored by professor Philip Zimbardo in Stanford University itself conducted the Stanford prison experiment (August 14-20, 1971). It was a social psychology experiment that focused on struggle between prisoners and prison officers. The college students were the subjects in this experiment. The experiment was funded by U.S. Office of Naval Research in order to find out the reason behind difficulties between prisoners and guards in United States Navy as well as United States Marine Corps.


  • The team selected total 24 participants in total, before selection a small test was conducted to make sure they are psychologically healthy and stable for the experiment.

  • Half of the subjects were given the role of guards and other half played the role of prisoners (nine plus three potential substitutes).

  • The setup was made as a mock prison with Zimbardo playing the role of superintendent.

  • The prison had one entrance covered in two fabricated walls. There was one cell wall too, to block the observation. Each cell was 6 x 9 feet of size.

  • Zimbardo’s primary reason was to observe the effect of rules and roles on people’s behavior.

  • Other focus was on power of group identity and situational validation, which generally people repulse.

  • It was made sure that the group of students selected did not have any criminal background, psychological problems or medical problems.

  • They were given $15 per day for participating in the experiment.


A day before starting the experiment the guards were given certain instructions:

  1. They were not allowed to harm the prisoners physically.

  2. They were not allowed to withhold their food and drinks.

  3. They were allowed to create some amount of fear and sense of boredom.

  4. Zimbardo also mentioned that the guards will have all the powers and prisoners will have none.

The guards were given a wooden stick to create sense of fear in the prisoners. Their clothing was made like the one of actual guards. They were also given whistle and mirrored sunglasses to prevent eye contact with the prisoners.

The prisoners on the other hand were given uncomfortable clothing and caps, as well as chain around the ankle. They were not allowed to wear any under clothing as well. The guards were instructed to call the prisoners by the number sewn on their uniforms and not by their actual names.

When prisoners were arrested they were strip-searched and were given new identities. The prisoners had to stay in the cell and yard all day whereas the guards only had to work an eight-hour shift and they could leave after the shifts were over.

Guards were given a very different environment to stay in; they got relaxation areas and proper rest time including other comforts. All the students quickly started adapting to their assigned roles. But it was observed that the guards, once the got the authority, became extremely hostile and started taking their roles too seriously. Guards seem to enforce their authority on the prisoners that led to serious psychological impact on students playing the role of prisoners. Some prisoners accepted the abuse while others tried to stop it and were harassed by the guards. The guards had different responses to their roles. One of the guards was described as most abusive one as he felt that his aggressive behavior will be a help in experiment. Another guard who initially applied for a prisoner wanted to help the prisoners because he felt sorry for them. He was asked to become tougher towards the prisoners.


It was observed that on second day prisoner started refusing to come out and follow the instructions of guards. Some guards’ volunteered to do extra shift, some attacked the prisoners with fire extinguishers. Guards also tried some psychological tactics like “privilege cell” for those prisoners who did not get involved in riots, but it was not successful. As the prisoners felt a bonding between them. After few more days the tension between guards and prisoners grew extensively. The guards started giving them punishment to make them suffer like urination or defecation in their own cell and did not allow them to clean it. Guards also removed the mattresses from their cell, due to which they had to sleep on floor. It was also observed that some guards became crueler than others and proved to inherit some genuine sadistic tendencies.

A newly admitted prisoner was abused when he showed concern towards the treatment of other prison mates. He was put into a closet and guards told other prisoners that he would only be released if they gave up their blankets and bare mattresses.

The experiment was planned for two weeks but was discontinued only after 6 days. Due to extremely harsh behavior of guards and prisoners.


Zimbardo concluded that the participants behaved that way because of the stimulated prison situation (the roles allotted to them) and not because of their own personality traits. The experiment was done to illustrate the cognitive dissonance theory and power of authority. The participants behaved more aggressively because they knew that they were being watched (Hawthorne effect).

Guards behaved so brutally that it left some prisoners with actual psychological damage. Three prisoners had to be released early. Zimbardo came to a conclusion that the guards and prisoners deeply absorbed their roles, which led to this situation. The guards would emotionally, mentally and physically humiliate the prisoners.


Lot of things related to this experiment has been found to be misleading and unscientific. Some say that Zimbardo instructed the guards to exert pressure on the prisoners psychologically. Some critics also say that this experiment might be a fraud. It was also written that this cannot be meaningfully described as an experiment and there were no real results for discussion. The experiment was also presumed to be unethical as most of the participants were forced to continue even after they wanted to withdraw from it. Although participants were told that they can leave whenever they wanted to but still Zimbardo did not allow this.