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The Stanford prison experiment
In 1971 Zimbardo's team ran a mock prison with students as guards and prisoners and stopped it after six days. Critics using the archive say the guards were coached. The researchers now call it a one-trial demonstration, not a traditional experiment.
- Where it sits
- Academic psychologyResearch published for other researchers and students.
- Evidence level
- ContestedThe evidence conflicts or is disputed, for example after failed replications.
- Sources inspected
- 6 of 62 with the relevant text, company document or archive item checked, 4 as an abstract or reference article, 0 not verified.
What happened
In 1971 Philip Zimbardo and colleagues at Stanford University ran a simulated prison in which students were assigned to guard or prisoner roles. It was planned as a two-week study and ended after six days. Zimbardo's study site says the guards became sadistic and the prisoners became depressed and showed signs of extreme stress.
The psychological idea
The study asked whether a prison role and setting could produce abusive behavior in ordinary people. Haslam and Reicher report that students were randomly assigned to the roles and that Zimbardo told the guards they could create boredom, fear and a sense of powerlessness, although they say he gave no direct orders.
In practice
No commercial use is documented. Le Texier examined the archive and interviewed 15 participants. He reports biased and incomplete data collection, guards receiving precise instructions on how to treat prisoners, guards not being told they were subjects, participants rarely becoming fully immersed, and support for earlier demand-characteristics criticisms. The BBC prison study, run by Reicher and Haslam over eight days, found that guards did not identify with their role and were reluctant to use authority.
Why it mattered
The study was long cited as showing that a toxic role alone can lead people to cruelty. Haslam, Reicher and Van Bavel argue from archival material that the experimenters encouraged the guards to adopt their roles and act tough, which fits identity leadership rather than automatic conformity to a role.
Limits and qualifications
A 2018 statement by Haney, Haslam, Reicher and Zimbardo calls both prison studies valid but best viewed as one-trial demonstration studies, not traditional experiments, and says behavior in both reflected many factors, including roles, norms, leadership and social identification. The BBC study is not a direct replication. The signatories say they have no definitive evidence of scientific fraud by any of them. Le Texier's claims are his reading of the archive, and Zimbardo's separate replies to him were not opened.
Evidence behind the claims
Zimbardo's study site says the experiment was conducted in 1971 at Stanford University, was a planned two-week investigation that had to be ended after six days, and that the guards became sadistic and the prisoners depressed with signs of extreme stress.
Haslam and Reicher report that students were randomly assigned to guard and prisoner roles and that Zimbardo told guards they could create boredom, fear and a sense of powerlessness, though they say he gave no direct orders.
Le Texier, using the archive and interviews with 15 participants, reports biased and incomplete data collection, precise instructions to guards, guards not told they were subjects, participants rarely fully immersed, and support for earlier criticisms such as demand characteristics.
Haslam, Reicher and Van Bavel argue from archival materials that the experimenters encouraged the guards to adopt their roles and act tough, consistent with identity leadership rather than automatic conformity to role.
In the eight-day BBC prison study the guards did not identify with their role, were reluctant to use their authority and were eventually overcome by the prisoners, and the authors argue that powerlessness and group failure make tyranny psychologically acceptable.
The 2018 statement signed by Haney, Haslam, Reicher and Zimbardo calls both studies valid but best viewed as one-trial demonstration studies rather than traditional experiments, says the BBC study is not a direct replication, and says behavior in both reflected many factors including roles, norms, leadership and social identification.
The signatories say they have no definitive evidence that any of them committed scientific fraud or deliberately misled others about their findings, and they regret ad hominem criticism.
People involved
- Philip Zimbardo. Lead researcher, Stanford University
- Craig Haney. Co-researcher and signatory of the 2018 consensus statement
- Thibault Le Texier. Author of the 2019 archive-based critique
- S. Alexander Haslam. Co-author of the BBC prison study and of critical reassessments
- Stephen Reicher. Co-author of the BBC prison study and of critical reassessments
In the Psy101 course
- OpenStax Psychology 2e, section 12.2: Self-presentationChapter 12, Social Psychology. Concept. The section discusses this topic.The reviewer opened the page: it describes the 1971 Stanford prison experiment, the guard and prisoner roles, and criticisms of recruitment and the guard guidelines.
This is course relevance only. It is not evidence for the historical or corporate claims on this page.See the full course map.
Sources and inspection
6 of 6 sources were opened and read at the level shown. A source marked as not verified supports no claim on this page by itself.
- [1]Consensus Statement on the Stanford Prison Experiment and BBC Prison StudyHaney, C.; Haslam, A.; Reicher, S.; Zimbardo, P.. Joint statement dated 27 August 2018, 2018. Report. Critique or replication.Relevant text checkedRead both pages of the two-page PDF as page images, including the eight numbered points and the signature block dated 27 August 2018.
- [2]Contesting the Nature of Conformity: What Milgram and Zimbardo's Studies Really ShowHaslam, S. A.; Reicher, S. D.. PLOS Biology, 10(11), e1001426, 2012. Journal article. Critique or replication.Relevant text checkedRead the open-access essay as returned by the fetch tool, for the Stanford prison passages. It argues for a social identity account and relies partly on the authors' own data.
- [3]Debunking the Stanford Prison ExperimentLe Texier, T.. American Psychologist, 74(7), 823-839, 2019. Journal article. Critique or replication.Abstract or publisher record onlyRead the abstract through the Europe PMC record. The article text was not opened.
- [4]Rethinking the nature of cruelty: The role of identity leadership in the Stanford Prison ExperimentHaslam, S. A.; Reicher, S. D.; Van Bavel, J. J.. American Psychologist, 74(7), 809-822, 2019. Journal article. Critique or replication.Abstract or publisher record onlyRead the abstract through the Europe PMC record. The article text was not opened.
- [5]Rethinking the psychology of tyranny: The BBC prison studyReicher, S.; Haslam, S. A.. British Journal of Social Psychology, 45(1), 1-40, 2006. Journal article. Critique or replication.Abstract or publisher record onlyRead the abstract text in the Crossref record. The article was not opened.
- [6]Stanford Prison Experiment (home page)Zimbardo, P. G.. prisonexp.org, 2018. Reference work. Primary source.Reference article readRead the study site's home page, which quotes Zimbardo. It is his own presentation, so it is self-report. It gives no participant numbers or guard instructions.
Access note: The original report and Zimbardo's replies to critics were not opened. Participant numbers, dates within 1971 and guard-behavior counts are therefore not stated. Three journal sources were read as abstracts only.
Independent source review: Claude review agent, independent of the research agent, 2026-10-21. Verdict: pass-with-edits.