· added 2026-10-07 current
Leadership, not just roles
A review emphasizes experimenter direction and identity leadership in explaining the guards’ behavior.
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Psychology concept
The Stanford prison experiment
ReinterpretedA 1971 study in which students played guards and prisoners in a mock prison. It became famous as proof that roles alone make people cruel. Archival research has since challenged that reading.
Reviewed 2026-10-07
In short
The Stanford prison experiment was a 1971 study in which 24 students were randomly assigned to be guards or prisoners in a mock prison; it was planned for two weeks and stopped after six days.
Classic conclusion: the situation, not personality, drove the guards' abuse.
Now: archival work argues the guards were coached toward harshness and knew what was expected. The original researchers maintain the study shows real situational dynamics. Even they call it a limited demonstration, not a traditional experiment.
The original study
The original study
In 1971 Philip Zimbardo and colleagues built a simulated prison at Stanford. Twenty-four students were randomly assigned to be guards or prisoners. The study was planned for two weeks and stopped after six days. The researchers used observation, video, questionnaires and interviews, and concluded that only a few reactions could be traced to personality differences. Official site FAQ ↗
How it's measured
This wasn't a measurement study with a control group. It was a single run of a simulation, recorded through observation, video, self-reports and interviews. The original researchers themselves describe it, and a later BBC study, as one-trial demonstrations rather than traditional experiments.
What the evidence says now
What the evidence says now
SettledThe basic facts: 24 students, random roles, stopped after six days. It's a single demonstration, not a controlled experiment.DebatedWhether the guards' behavior came from the roles themselves, or from instructions, coaching and expectations set by the researchers.UnknownHow the findings would carry over to real prisons and real institutions.
1971 OriginalStudents in a simulated prison; roles assigned at random; the researchers attributed few reactions to personality. Source ↗
2018 ContextThe researchers' own statement: both prison studies were limited one-trial demonstrations, and the BBC Prison Study was not a direct replication. Source ↗
2019 ChallengeA study found support for the possibility that the wording of the guards' orientation encouraged abuse. Source ↗
2019 ChallengeAn archival analysis argued that the experimenters encouraged guards to adopt their roles and act tough. Source ↗
2020 DefenseIn a comment in American Psychologist, Zimbardo and Haney maintained the study demonstrates destructive dynamics in dehumanizing environments. Zimbardo's published response on the official site argues the critiques don't change its main conclusion. Source ↗
2024 ChallengeAn archive-based book that also interviewed about half the participants argues the guards knew what was expected and were trained and supervised. Source ↗
2025 RefinesA review emphasizes experimenter direction and leadership in shaping the guards' behavior. Source ↗
Common misunderstandings
"It proved anyone becomes cruel in a uniform." That strong reading is disputed; the researchers' influence on the guards is a central question.
"It was replicated by the BBC." The 2002 BBC Prison Study was related but, by its authors' own account, not a direct replication.
"It was a controlled experiment." It was a single run with no control group, a demonstration.
Try it
Read the official site's summary and one critique. For each, list the evidence it relies on: video, interviews, archives or recordings. Where do they disagree about facts, not just interpretation?
Done when: you've named one factual disagreement.
Questions people ask
What was the Stanford prison experiment?
A 1971 simulation where 24 students were randomly made guards or prisoners. It was planned for two weeks and stopped after six days.
Did it show ordinary people naturally turn cruel?
That is the famous claim, and it is disputed. Archival research argues the guards were coached and knew what was expected; the original researchers maintain the situation mattered.
Was it fake?
Critics document serious problems with its methods and with how it was presented. The sources don't support a single agreed verdict of fraud, and the researchers still defend it as a limited demonstration.
Was it ever repeated?
A related BBC study ran in 2002 (published 2006), but its authors say it wasn't a direct replication. It reached different conclusions about groups and leadership.
Was it ethical?
It wouldn't pass modern ethics review in its original form. The official site itself raises the question of whether participants' suffering was justified.
Learn more
- Rethinking the infamous Stanford prison experiment
researchers explain the leadership and identity interpretation in plain language
- The official Stanford Prison Experiment site
The original researchers’ side.
- Noba: Conformity and Obedience
The wider social-influence background.
- OpenStax: Self-presentation
The classic textbook account; read it alongside the critiques, as it states the conclusion more strongly than the evidence now supports.
- MIT 9.70 Social Psychology
Older course (2013); useful context.
What changed
· added 2026-10-07 current
Participants revisit the experiment
Coverage of a 2024 documentary series where participant interviews complicate or contradict the familiar account.
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· added 2026-10-07 current
A book-length archival investigation
Drawing on archives and interviews with about half the participants, it argues the guards were trained and supervised.
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Sources
Part of Psychology: Development, social behavior and personality