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Stanford prison experiment
1971; exposed as coached, 2018· Finding or experiment
Weak or failed to replicateFamous but not holding up in careful repeats.
Philip Zimbardo's 1971 mock prison study, long taught as proof that roles turn people cruel, now known to be coached and flawed.
See it on the Psychology map →What it says
In August 1971, Zimbardo had two dozen male students randomly assigned as guards or prisoners in a Stanford basement. Some guards became abusive; Zimbardo, acting as prison superintendent, stopped the planned two-week study after six days when graduate student Christina Maslach objected. In 2018, archival recordings and interviews showed staff had urged guards to be tough, one guard said he was playing a role, and a prisoner said his breakdown was partly faked.
Why it matters
For decades it shaped textbooks and films, and Zimbardo cited it in 2004 testimony about Abu Ghraib; its unraveling became a lesson in checking dramatic studies before trusting them.
The evidence
Thibault Le Texier's 2018 book and 2019 article drew on Stanford's archives. A 2002 BBC partial replication found guards did not spontaneously turn tyrannical. It never had a control group.
Open questions
Zimbardo, who died in 2024, defended it as a demonstration. Researchers debate whether any lesson survives, such as how leaders encourage cruelty.
Connections (2)
▸The replication crisis re-examined Stanford prison experimentWell replicated
The connection
The crisis taught psychologists to recheck famous studies. The Stanford prison experiment was never a controlled experiment, and in 2018 researchers reading its archives found coaching of guards and staged behavior. Textbooks that had treated it as proof of situational evil began cutting or qualifying it.
Who showed it and when
Stanford University archives; French researcher Thibault Le Texier's 2018 book and journalist Ben Blum's 2018 article; follow-up analyses in American Psychologist in 2019.
The evidence
Original recordings released by Stanford capture the warden urging a reluctant guard to be 'tough.' Zimbardo's 2018 reply disputed the interpretation, not the recordings.
Open questions
Critics raised demand effects as early as 1975, so some ask why textbooks took so long to change, and which other classic demonstrations deserve the same audit.
▸Stanford prison experiment was long cited as proof of Social influence: conformity and obedienceWeak or failed to replicate
The connection
For decades textbooks used the study to argue that social roles alone can turn ordinary people cruel, the strongest version of situational influence. Zimbardo applied this to Abu Ghraib in 2004. Archival evidence of coaching and role-playing means it no longer counts as evidence for that claim.
Who showed it and when
Stanford University, August 1971; Zimbardo's testimony for an Abu Ghraib guard's defense and his 2007 book The Lucifer Effect.
How solid is it?
Analyses in 2018–2019 showed guards were urged to be tough, and a 2007 study found that ads for a 'prison life' study attracted more aggressive volunteers.
Open questions
Real prisons do produce abuse, so researchers debate what actually drives it: roles, leadership, institutional culture or who is recruited.