The Stanfor prison experiment was a study of the psychological effects of becoming a prisoner or prison guard. The experiment was conducted in 1971 by a team of researchers led by psychologist Philip Zimbardo at Stanford University. Twenty-four undergraduates were selected out of 70 to play the roles of both guards and prisoners and live in a mock prison in the basement of the Stanford psychology building. The students who were assigned to be the prisoners were paid $15 a day as an incentive, which is worth about $80 per day in 2008 currency.