A 1971 study led by Philip Zimbardo at Stanford University in which college student volunteers were randomly assigned to play prisoners or guards in a simulated prison, intended to examine how institutional roles and situational forces shape behavior; it became one of psychology's most famous studies and one of its most disputed.
Facts
Disputed
Key FindingZimbardo concluded that the prison-like situation itself, not the individual personality traits of the participants, caused the guards' abusive behavior and the prisoners' distress, though later archival research disputes how spontaneous that behavior really was. 1 Zimbardo's own situational-causation reading is the study's famous conclusion, but the finding is now heavily disputed; see the linked open question. Cross-Tradition Connections
Sources
1. Wikipedia: Stanford prison experiment
Wikimedia FoundationInterpretation and reproducibility of results sectionQuote, Interpretation and reproducibility of results section
the simulated-prison situation, rather than individual personality traits, caused the participants' behavior
1. Wikipedia: Stanford prison experiment
Wikimedia FoundationLead sectionQuote, Lead section
1971
1. Wikipedia: Stanford prison experiment
Wikimedia FoundationCritiques of scientific validityQuote, Critiques of scientific validity
the guards were asked directly to behave in certain ways in order to confirm Zimbardo's conclusions, which were largely written in advance
Open Questions (1 open question)
Did the Stanford Prison Experiment reveal a genuine, spontaneous psychological effect of institutional roles, or did the guards' abusive behavior result substantially from Philip Zimbardo's own coaching and demand characteristics rather than emerging naturally from the prison situation itself?
Zimbardo's own recordings and instructions to guards, later examined by historian Thibault Le Texier through the Stanford archives, show guards were directly coached toward the study's expected conclusions before the results were interpreted as a spontaneous emergent effect; the original study also had no control condition and was never formally peer reviewed, making it difficult to separate genuine situational influence from guided performance.
What would resolve this A controlled replication with genuinely blind, uncoached participant instructions and pre-registered analysis, which the ethical concerns the original study itself raised make difficult to conduct today.
Social psychology, research methodology, and the history of science.Wikipedia: Stanford prison experiment
Dissenting Readings (1 dissenting reading)
Key Finding
French historian Thibault Le Texier's 2018 archival research into Zimbardo's own recordings and instructions argues the standard reading overstates a spontaneous finding: guards were directly told how the experimenters wanted them to behave before results were interpreted as an emergent effect of the prison situation itself, so the abusive behavior may reflect participants performing to a script and to Zimbardo's own expectations more than a genuine, unprompted psychological transformation.
A dissenting reading, from Thibault Le TexierWikipedia: Stanford prison experiment, Wikimedia Foundation
Frequently Asked Questions
Was the Stanford Prison Experiment conducted in a real prison?
No, it was a simulated prison.
The 1971 study built a simulated prison in the basement of a Stanford University psychology building for the two week study. The prisoners and guards were paid student volunteers randomly assigned to their roles, not actual inmates or correctional officers.
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