Zimbardo's Experiment By naadrosli Aug 14, 1971 First Day of Experiment 24 out of 75 male students selected. Selected to take on randomly assigned roles of prisoners and guards. Aug 14, 1971 Assigning The Roles 12 were assigned as prisoners 12 were assigned as guards They were receiving $15 per day for 7 to 14 days Aug 20, 1971 Experiment Ended