The Zimbardo Prison Experiment in 1971 was originally designed for a two-week time period, but ran only for six days. The reason for the early termination of the experiment was because the guards had begun to systematically abuse the prisoners through ridicule, verbal abuse, and other forms of severe treatment. The study was criticized for not informing participants about the risk of psychological stress, physical discomfort, and/or humiliation to which they were ultimately exposed.