Stanford Prison Experiment: Zimbardo’s Famous Social Psychology Study

The Stanford prison experiment was a social psychology study which demonstrated the horrors people can inflict on one another.

Stanford prison experiment

The Stanford prison experiment was a social psychology study which demonstrated the horrors people can inflict on one another.

The Stanford prison experiment was run to find out how people would react to being made a prisoner or prison guard.

The psychologist Philip Zimbardo, who led the Stanford prison experiment, thought ordinary, healthy people would come to behave cruelly, like prison guards, if they were put in that situation, even if it was against their personality.

It has since become a classic study, studied by generations of psychology students and recently coming under a lot of criticism.

What was the Stanford prison experiment about?

The Stanford prison experiment asks timeless questions about human nature, like what makes a person evil?

Can a good person commit evil acts?

If so, what can make people cross the line?

Is there some set-point which when crossed unleashes the evil?

Or is it something about the situations in which people are placed that determines our behaviour?

The famous ‘Stanford Prison Experiment’ – argues a strong case for the power of the situation (Zimbardo, 1971).

Not only that but the experiment has also inspired a novel, two films, countless TV programs, re-enactments and even a band.

More on that later, first the experiment.

The procedure of the Stanford prison experiment

The idea was simple: to see how ordinary men, chosen to be the most healthy and ‘normal’ would respond to a radical change to their normal roles in life.

Half were to become prison guards, the other half their prisoners. In this experiment there were no half-measures, for it to be effective it had to closely approximate the real experience of prisoners and guards.

These participants in the Stanford prison experiment were in for the ride of their lives.

‘Prisoners’ were ‘arrested’ by a police car with sirens wailing while they were out going about their everyday business.

Then they were fingerprinted, blindfolded and put in a cell, then stripped naked, searched, deloused, given a uniform, a number and had a chain placed around one foot.

The other participants were made into guards who wore uniforms and were given clubs.

A prison was mocked up in the basement of a Stanford University building.

And so the Stanford prison experiment began.

Rebellion crushed

All was quiet until the second day when the ‘prisoners’ rebelled against their incarceration.

The guard’s retaliation was swift and brutal.

Guards stripped the prisoners naked, removed the beds from the prison, placed the rebellion’s ringleader in solitary confinement and began harassing all the ‘prisoners’.

Soon the ‘prisoners’ began behaving with blind obedience towards the prison guards.

After only a few day’s realistic role-playing participants reported it felt as though their old identities had been erased.

They had become their numbers.

So too had the ‘guards’ taken on their roles – taunting and abusing their prisoners.

Even the lead researcher, Philip Zimbardo, admits he became submerged in his role as the ‘prison superintendent’.

In fact, Zimbardo believes the most powerful result of the Stanford prison experiment was his own transformation into a rigid institutional figure, more concerned with his prison’s security than the welfare of his participants.

Other members of the experimental team became engrossed in their new role.

Craig Haney, like Zimbardo, explained he became completely engaged in the day-to-day crises they were facing in running the ‘prison’ and forgot about the aim of the Stanford prison experiment.

Playing the roles

It was only when one of his colleagues intervened that the Stanford prison experiment was finally stopped.

In total it only lasted six of the planned 14 days.

Young men previously found to be pacifists were, in their roles as guards, humiliating and physically assaulting the ‘prisoners’ – some even reported enjoying it.

The ‘prisoners’, meanwhile, quickly began to show classic signs of emotional breakdown.

Five had to leave the ‘prison’ even before the experiment was prematurely terminated.

The psychological explanation for the participant’s behaviour was that they were taking on the social roles assigned to them.

This included adopting the implicit social norms associated with those roles: guards should be authoritarian and abuse prisoners while prisoners should become servile and take their punishment.

Inevitably the Stanford prison experiment has attracted criticism for being unethical, involving a small sample size, lack of ecological validity and so on.

Despite this it’s hard to deny that the experiment provides important insights in to human behaviour, perhaps helping to explain the abuses that occurred in situations like the Abu Ghraib Prison.

Conclusions of the Stanford prison experiment

The Stanford prison experiment showed how people are ready to conform to the roles they are given and expected to play.

They lost their identity within the group, taking the cue from what other people were doing.

The situation of the prison turned guards into sadists and reduced their sense of identity and personality responsibility.

The prisoners were also surprised how much it changed their behaviour.

Even assertive types became submissive and weak when placed in the role of a prisoner in the Stanford prison experiment.

In this sense it showed that the situation was more powerful in guiding people’s behaviour than their personality.

Is the Stanford prison experiment realistic?

Does this Stanford prison experiment mirror what occurs in real prisons?


Writing in Inside Rikers: Stories from the World’s Largest Penal Colony, Jennifer Wynn interviews prison guards from New York City’s largest penal colony, Rikers Island.

One captain explained that guards easily become used to the level of violence inflicted on inmates – it’s part of the job and they soon become immune.

Some can’t understand how they become different people at work.

Levels of violence against prisoners were so bad in one unit, called the ‘Central Punitive Segregation Unit’ of Rikers’, that almost a dozen guards were officially charged with assaulting inmates in 1995.

Eventually the inmates won $1.6 million dollars in compensation.

This is just one example.

Criticism of the Stanford prison experiment

Other the years, many criticism have been thrown at the Stanford prison experiment, including:

  • The guards later claimed they were acting in the Stanford prison experiment: psychologists refer to this as the demand characteristics of the study.
  • The prisoners and guards were playing a role so you cannot generalise to real life. Different factors may affect people’s behaviour in real life. The Stanford prison experiment’s prison itself was not that realistic and people knew they were not in prison.
  • Because of its ethics, the study could not be conducted nowadays. It would not pass any standard psychological ethics committees. For example, participants did not agree to be ‘arrested’ at their homes.
  • Subsequent studies have cast doubt on the validity of the Stanford prison experiment, suggesting that participants ‘faked’ their behaviour and tried to help the experimenters (Texier, 2019).

Popular culture and the Stanford Prison Experiment

The study is now so well-known it has crossed over into popular culture. It has inspired a novel, Das Experiment by Mario Giordano, which was later filmed, and a new movie by the writer of the Usual Suspects is slated for filming.

The experiment has also been covered or recreated in countless TV shows, most notably on the BBC.

Not only this, but the experiment has even inspired the name of a band.

‘Stanford Prison Experiment’ released their first eponymously titled album in 1994, following up a year later with ‘The Gato Hunch’.

What other psychology study can say it’s got a band named after it?

→ This post is part of a series on the best social psychology experiments:

  1. Halo Effect: Definition And How It Affects Our Perception
  2. Cognitive Dissonance: How and Why We Lie to Ourselves
  3. Robbers Cave Experiment: How Group Conflicts Develop
  4. Stanford Prison Experiment: Zimbardo’s Famous Social Psychology Study
  5. Milgram Experiment: Explaining Obedience to Authority
  6. False Consensus Effect: What It Is And Why It Happens
  7. Social Identity Theory And The Minimal Group Paradigm
  8. Negotiation: 2 Psychological Strategies That Matter Most
  9. Bystander Effect And The Diffusion Of Responsibility
  10. Asch Conformity Experiment: The Power Of Social Pressure


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This site is all about scientific research into how the mind works.

It’s mostly written by psychologist and author, Dr Jeremy Dean.

I try to dig up fascinating studies that tell us something about what it means to be human.

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Author: Jeremy Dean

Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology. He has been writing about scientific research on PsyBlog since 2004. He is also the author of the book "Making Habits, Breaking Habits" (Da Capo, 2013) and several ebooks.