Stanford Prison Experiment

The Stanford Prison Experiment was an experiment conducted by psychology professor Philip Zimbardo and a team of researchers in 1971. Funded by the United States Office of Naval Research, it was designed to uncover the sources of problems between prisoners and prison guards. The study is frequently cited as an example of how quickly normal people give into authoritarian urges when given a small amount of power. Zimbardo believed that certain personality traits were associated with abusive tactics in prison, but his experiment demonstrated that seemingly psychologically healthy people would quickly use abusive tactics to maintain power.

How Did the Study Work?
Twenty-four students were randomly assigned the roles of prisoner or prison guard. The prisoners were “arrested” prior to their incarceration, and the entire experiment aimed to mimic the realities of prison life as neatly as possible.

What Happened During the Study?
The students participating in the study immediately adapted to their new roles, with guards adopting draconian, authoritarian measures. Some of the prisoners were subjected to psychological torture. Many of the prisoners not only accepted the abuse, but also abused other prisoners at the direction of the guards and in attempts to acquire favor with the guards. Zimbardo acted as prison warden during the experiment, and he, too, was affected by the experiment, permitting the abuse to continue.

As the experiment progressed to the second day, several prisoners lead a riot, prompting the guards to institute extremely authoritarian measures to crush dissent.

Zimbardo abruptly ended the experiment after only six days, despite the fact that the experiment was scheduled to continue for two weeks. A graduate student who went to the prison to observe the experiment objected to prison conditions and told Zimbardo she found the experiment immoral. Of the 50 or more people who observed the experiment, this student was the only one to object.

The experiment serves as strong support that context, rather than innate personality traits, influences behavior. It is often cited as evidence of the dangers of giving excessive authority to any one person or entity.


  1. The Stanford Prison Experiment. (n.d.).  A Simulation Study of the Psychology of Imprisonment. Retrieved July 24, 2012, from
  2. The Stanford Prison Experiment: Still powerful after all these years (1/97). (n.d.). The Stanford Prison Experiment: Still Powerful after All These Years (1/97). Retrieved July 24, 2012, from
  3. Zimbardo, P. G. (n.d.). The Stanford Prison Experiment. A Simulation Study of the Psychology of Imprisonment. Retrieved July 24, 2012, from

Last Updated: 08-26-2015

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