On August 20, 1971, Zimbardo announced the end of the experiment to the participants.
According to Zimbardo's interpretation of the SPE, it demonstrated that the simulated-prison situation, rather than individual personality traits, caused the participants' behavior. Using this situational attribution, the results are compatible with those of the Milgram experiment, where random participants complied with orders to administer seemingly dangerous and potentially lethal electric shocks to a shill.
The experiment has also been used to illustrate cognitive dissonance theory and the power of authority.
Participants' behavior may have been shaped by knowing that they were watched (Hawthorne effect). Instead of being restrained by fear of an observer, guards may have behaved more aggressively when supervisors observing them did not step in to restrain them.
Zimbardo instructed the guards before the experiment to disrespect the prisoners in various ways. For example, they had to refer to prisoners by number rather than by name. This, according to Zimbardo, was intended to diminish the prisoners' individuality. With no control, prisoners learned they had little effect on what happened to them, ultimately causing them to stop responding, and give up. Quick to realize that the guards were the highest in the hierarchy, prisoners began to accept their roles as less important human beings.
One positive result of the study is that it has altered the way US prisons are run. For example, juveniles accused of federal crimes are no longer housed before trial with adult prisoners, due to the risk of violence against them.
Shortly after the study was completed, there were bloody revolts at both the San Quentin and Attica prison facilities, and Zimbardo reported his findings on the experiment to the U.S. House Committee on the Judiciary.