In August 1971, Stanford University psychology professor Philip Zimbardo launched a two-week simulation of prison life using 24 male college students, randomly assigned as either guards or prisoners. Recruited through a newspaper advertisement, participants were paid $15 a day. Within days, the guards, given uniforms designed to strip individual identity, began psychologically abusing the prisoners with escalating cruelty.
The experiment collapsed on the sixth day after psychologist Christina Maslach visited the site and confronted Zimbardo over the conditions she witnessed. He shut it down, later admitting he had become too absorbed in his own role as superintendent. The study became a landmark case in research ethics, prompting American universities to strengthen institutional review processes for human experimentation. Later critics, including researcher Thibault Le Texier, argued the guards had been coached to behave aggressively, and that Zimbardo’s conclusions were largely written before the experiment began.
