The Stanford prison experiment was ostensibly a psychological study of human responses to captivity and its behavioral effects on both authorities and inmates in prison. It was conducted in 1971 by a team of researchers led by Philip Zimbardo of Stanford University. Undergraduate volunteers played the roles of both guards and prisoners living in a mock prison in the basement of the Stanford psychology building. Prisoners and guards rapidly adapted to their roles, stepping beyond the boundaries of what had been predicted and leading to dangerous and psychologically damaging situations. One-third of the 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.