In 1971, psychologist Philip Zimbardo built a mock prison in the basement of the Stanford Psychology Department and invited two dozen students to play the roles of either a prisoner or a guard. After 6 days he was forced to halt his observational study because many of the guards had become so abusive toward the prisoners that he feared for their safety (Haney, Banks, & Zimbardo, 1973).

PHILIP G. ZIMBARDO, INC.