What was the Stanford Prison Experiment?
The Stanford Prison Experiment was a 1971 study led by Stanford psychologist Philip Zimbardo. Twenty-four male college students recruited through a newspaper ad were randomly assigned to be guards or prisoners in a mock prison built in the basement of the psychology building.
- Researchers
- Philip Zimbardo and colleagues
- When
- August 1971
- Participants
- 24 male college students (guards, prisoners, alternates)
- Outcome
- Planned for two weeks, stopped after six days
What happened
- "Prisoners" were "arrested" at home with help from the local police and brought to the mock prison.
- Prisoners wore smocks and were called by numbers; guards got uniforms and mirrored sunglasses.
- After a prisoner rebellion on day two, guards increasingly used humiliating punishments and control.
- Several prisoners showed acute emotional distress and were released early.
- Christina Maslach, a graduate student visiting the study, objected strongly, and Zimbardo ended it after six days.
Zimbardo’s conclusion: the power of the situation
Zimbardo argued that ordinary students became cruel simply because of the situation they were in. He claimed that evil behavior stems less from personality than from roles, uniforms and power, and from the systems that create them, and he later cited the study when testifying about abuses at Abu Ghraib prison in Iraq.
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Criticisms and reassessment
For decades the study appeared in introductory textbooks, but it is now widely regarded as scientifically weak.
| Criticism | Details |
|---|---|
| Coaching of guards | Le Texier (2019) used archival recordings and documents to show guards were encouraged to be "tough." |
| Demand characteristics | Participants may have guessed what the researchers wanted and acted accordingly. |
| Dual role | Zimbardo acted as both lead researcher and "prison superintendent," compromising objectivity. |
| Sample and design | A small sample with no real control condition limits what can be concluded. |
| Ethics | Participants suffered serious psychological distress. |
Not every guard became abusive, either: some were fair and a few helped prisoners. Many psychologists now emphasize what authorities expect and permit, and how strongly people identify with a group’s goals, rather than the idea that anyone automatically turns cruel.
Legacy for research ethics
Together with the Milgram obedience experiments, the study became a landmark case for protecting research participants. Modern psychology research in the US requires Institutional Review Board (IRB) approval under federal human-subjects rules, informed consent, and the right to withdraw at any time.
Frequently asked questions
- What was the Stanford Prison Experiment?
- A 1971 study in which Philip Zimbardo had students play guards and prisoners in a mock prison; it was stopped after six days as abuse escalated.
- Was the Stanford Prison Experiment fake?
- Archival analysis, notably Le Texier (2019), indicates guards were coached toward harsh behavior, so its original conclusions are widely questioned.
- What is the lesson of the Stanford Prison Experiment?
- Roles, power and authority expectations can shape behavior, and research participants must be protected by strong ethical safeguards.
References
- Haney, C., Banks, C., & Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology and Penology, 1, 69–97.
- Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7), 823–839.
- Zimbardo, P. (2007). The Lucifer Effect: Understanding How Good People Turn Evil. New York: Random House.