Another massively controversial psychological study is Zimbardo’s Stanford Prison Experiment, one of the most criticised experiments in modern psychology.

In the experiment, university students were chosen to play the roles of prisoners or prison guards in a fake prison environment; the aim of the study was to test their theory that the often-violent behaviour of prison guards was due to their personality traits rather than their environment. Although this was a commendable aim, the problem with this study lay in its realism and design- the simulation was so effective that both the participants and the experimenters became too involved and could not see how unethical the situation had become.

While the study was supposed to last two weeks, it had to be stopped after just 6 days as the participants were playing their roles too well. Some of the prison guards had become violent, even showing sadistic tendencies and torturing prisoners, while the prisoners had become passive and accepting, forgetting the situation was not real and they did not deserve the treatment. One prisoner even had to be removed after suffering a nervous breakdown on day 3.

This may sound like the experiment was just conducted on violent or unstable people, but in fact the opposite is true; the participants were all middle-class university students, specifically selected because they had perfect psychological health. The results of the experiment were incredibly valuable despite its problems, because they showed that cruel behaviour was not simply caused by someone being a “bad” or violent person. Instead, people put into extreme situations responded in extreme ways, especially if there were contributing factors such as the processes of depersonalisation and deindividuation.

This study, along with Milgram’s  research, demonstrated how authority and social environment affected behaviour, a theme which has been present and debated in psychology ever since.