The Stanford prison experiment was a study of the psychological effects of becoming a prisoner or prison guard. The experiment was conducted from August 14 to 20, 1971 by a team of researchers led by Psychology professor Philip Zimbardo at Stanford University. It was funded by a grant from the U.S. Office of Naval Research and was of interest to both the US Navy and Marine Corps in order to determine the causes of conflict between military guards and prisoners.

Twenty-four students were selected out of 75 to play the prisoners and live in a mock prison in the basement of the Stanford psychology building. Roles were assigned randomly. The participants adapted to their roles well beyond what even Zimbardo himself expected, leading the “Officers” to display authoritarian measures and ultimately to subject some of the prisoners to torture. In turn, many of the prisoners developed passive attitudes and accepted physical abuse, and, at the request of the guards, readily inflicted punishment on other prisoners who attempted to stop it. The experiment even affected Zimbardo himself, who, in his capacity as “Prison Superintendent,” lost sight of his role as psychologist and permitted the abuse to continue as though it were a real prison. Five of the prisoners were upset enough by the process to quit the experiment early, and the entire experiment was abruptly stopped after only six days. The experimental process and the results remain controversial.

The results of the experiment are said to support situational attribution of behavior rather than dispositional attribution. In other words, it seemed the situation caused the participants’ behavior, rather than anything inherent in their individual personalities. In this way, it is compatible with the results of the also-famous Milgram experiment, in which ordinary people fulfilled orders to administer what appeared to be agonizing and dangerous electric shocks to a confederate of the experimenter.