The Stanford prison experiment (SPE), also referred to as the Zimbardo prison experiment (ZPE), was a controversial psychological experiment performed in August 1971 at Stanford University. It was designed to be a two-week simulation of a prison environment that examined the effects of situational variables on participants' reactions and behaviors. Stanford University psychology professor Philip Zimbardo managed the research team who administered the study. Zimbardo ended the experiment early after realizing the guard participants' abuse of the prisoners had gone too far.