The Stanford prison experiment was a human experiment to psychologically study the human responses to captivity - half the subjects had to play the role of inmates, and the other half prison guards, living in a prison environment. The experiment was conducted by Philip Zimbardo of Stanford University in 1971. The inmates and prison guards adapted to their roles and even stepped beyond the boundaries of what had been predicted, which lead to psychologically damaging and dangerous situations. One-third of the prison guards were judged to have exhibited “genuine” sadistic tendencies, while many prisoners were emotionally traumatized and two had to be removed from the experiment early. Finally, Zimbardo, alarmed at the increasing abuse and anti-social behaviour, terminated the experiment earlier than intended.