Power, prisons and psychology: A look back at Stanford Prison Experiment that Netflix is recreating

In 1971, students handed power as prison guards stripped and humiliated their peers within days. Netflix is recreating the study, now widely disputed.

In 1887, the British historian Lord Acton wrote that "power tends to corrupt, and absolute power corrupts absolutely". For decades, an experiment held at Stanford University in 1971 was treated as scientific proof of his point.

Netflix's unscripted series The New Stanford Prison Experiment places 30 volunteers inside a real prison. (AFP)

Netflix is now recreating that experiment, one of the most famous, and most disputed, in psychology. Its unscripted series The New Stanford Prison Experiment, which starts streaming on October 21, places 30 volunteers inside a real prison and randomly assigns them to be guards or prisoners, Variety has reported. The show's executive producer, Jane Lipsitz, told Variety that the original study – simply called the Stanford Prison Experiment – had “serious ethical flaws” but raised a question that matters even more today.

The experiment

In the summer of 1971, Philip Zimbardo, a psychology professor at Stanford University in California, placed an advertisement in a local newspaper. It asked for volunteers for a study of prison life that would last up to two weeks and pay $15 a day.

Zimbardo wanted to find out whether the situation people are put in, more than their own character, decides how they behave.

The "prison" was a windowless corridor in the basement of the university's psychology department. Small offices fitted with barred doors served as cells, and a closet was used for solitary confinement.

Zimbardo ran the experiment and also played the prison's superintendent. He later called this double role "a serious error in judgment", because the person responsible for the volunteers' welfare was also the one running the prison. Two psychology graduate students, Curtis Banks and Craig Haney, helped him.

Haney later became a psychology professor at the University of California, Santa Cruz, and an expert on prison conditions.

Six days in the basement

On a Sunday morning in August, Palo Alto police arrested the "prisoners" at their homes, handcuffed and searched them, and processed them at the police station as they would real suspects. They then handed them over to the researchers.

In the basement, each prisoner had to wear a smock with a number on it and no underwear, a chain around one ankle, and a nylon stocking over his hair to look like a shaved head. The guards were to call prisoners only by their numbers.

The guards wore military-style uniforms and mirrored sunglasses, and carried batons. On the second day, the prisoners rebelled, tearing off their numbers and barricading themselves in their cells. The guards called in their off-duty colleagues and broke up the protest. They then punished the prisoners by stripping them, locking them in solitary confinement, taking away meals, blankets and pillows, and ordering push-ups. They also woke the prisoners several times a night for head counts. Zimbardo wrote that the worst abuse came on the late-night shift, when guards thought no one was watching.

Within 36 hours of the arrests, Prisoner 8612 was crying, screaming and cursing, and the researchers let him go. Four more prisoners were released over the following days, one of them after breaking out in a rash across his body. One of the replacement prisoners, brought in midweek, later said the basement had become "a prison run by psychologists instead of run by the state".

On the fifth night, a Thursday, Christina Maslach visited the basement. She had just finished her doctorate in psychology at Stanford and was dating Zimbardo; they married the following year. She watched the guards march the prisoners to the toilet in a chained line, with paper bags over their heads. Afterwards, she recalled, she told Zimbardo something like: "What you are doing to those boys is a terrible thing!" After a heated argument, Zimbardo agreed to stop. The experiment ended the next morning, six days into the two weeks it was meant to run.

The above account comes from Zimbardo, Maslach and Haney, who described those six days in their own words, in a chapter they wrote together for the experiment's 25th anniversary titled Reflections on the Stanford Prison Experiment.

Zimbardo concluded that the situation had turned healthy young men into abusive guards and broken prisoners, writing that in less than a week "they had become totally different creatures". He defended that conclusion for the rest of his life.

On the experiment's 50th anniversary in 2021, he wrote that it showed how good people can be drawn into evil, including what he called "the evil of inaction": doing nothing when they should act.

The controversies

Over time, Zimbardo admitted some of the experiment's ethical failings himself. In account written for the experiment's 25th anniversary in 1996, he wrote that it was unethical because people suffered, and others were allowed to humiliate them for days. He also wrote that "we did not end the study soon enough".

In his view, it should have been stopped on the second day, when the first prisoner broke down, and his double role as researcher and superintendent had kept him from doing so. In the same account, Haney described a nightmare in which he himself was locked in the prison, and wrote that he pressed on regardless: "After all, we had a prison to run." In 2018, Zimbardo wrote that the experiment's major flaw was that "it had no independent scientific observer", because he had been absorbed in running the prison.

The joint account also said that neither the guards nor the prisoners were told how to behave, and that the guards were told only to keep order and not to use their batons as weapons.

In a 2019 paper in the psychology journal American Psychologist, Thibault Le Texier, a French social scientist, compared these accounts with Zimbardo's own records of the experiment, which Zimbardo had given to Stanford's library and which include notes, recordings and the participants' reports.

Le Texier found that at a briefing the day before the arrests, Zimbardo told the guards they could create boredom, fear and a sense of powerlessness in the prisoners. The undergraduate who played the prison warden gave the guards ideas, such as long, humiliating head counts. He took them from a mock prison that he and other students in Zimbardo's class had staged in a university hostel three months earlier. Eleven of the experiment's 17 prison rules were copied from that student exercise. In one recording, the warden tells a guard who had been holding back that every guard needed to be "tough".

Le Texier also found that the plan Zimbardo sent to Stanford's ethics committee for approval said prisoners would be led to believe they could not leave, except in an emergency. Two prisoners who asked to quit on the second day were turned down. Le Texier called the experiment "an incredibly flawed study that should have died an early death".

The harshest guard worked the night shift and was nicknamed "John Wayne", after the Hollywood cowboy actor. According to Maslach, he put on a Southern American accent copied from a character in a prison film. When the experiment ended, he told the warden he had been acting all along.

The original advertisement itself may also have drawn a particular kind of volunteer. In 2007, two psychologists at Western Kentucky University in the US placed two advertisements in university newspapers that were identical except that one mentioned "prison life". The men who answered the prison advertisement scored higher on personality tests for aggression, authoritarianism (a preference for strict obedience to authority) and narcissism, and lower on empathy, than those who answered the other. The authors cautioned that what this meant for the Stanford experiment could only be guessed at.

Zimbardo rejected Le Texier's main criticisms. In 2018, he said the guards had been given no formal or detailed instructions and had been barred from using force.

The experiment’s impact on psychology

For decades, psychology students were taught the Stanford Prison Experiment as proof that ordinary people can turn cruel when given power over others. Le Texier found that most textbooks went on teaching it that way while leaving out its critics.

The experiment is also often cited as one reason the US tightened its rules for research involving people. Two British social psychologists, Stephen Reicher and Alex Haslam, have argued that the controversy stopped large studies of this kind for decades.

When photographs of US soldiers abusing Iraqi detainees at the US-run Abu Ghraib prison near Baghdad became public in 2004, Zimbardo argued that conditions inside the prison explained much of what the soldiers did. He testified for the defence at the military trial of Staff Sergeant Ivan "Chip" Frederick, who ran the prison's night shift. Frederick was sentenced to eight years. In 2007, Zimbardo published The Lucifer Effect, a book on the Stanford experiment and on how, in his view, good people come to do evil.

In 2025, Augustine Brannigan, a sociologist at the University of Calgary in Canada, asked on Retraction Watch, a website that tracks withdrawn scientific papers, whether the experiment should be formally withdrawn from the scientific record. He concluded that the realistic hope was for textbooks to describe it more responsibly.

The other attempts

In 1979, researchers in Australia ran mock prisons in three different ways. Guards and prisoners turned hostile only under the strict regime modelled on real prisons, and stayed far calmer where guards were encouraged to treat prisoners with respect. Zimbardo said the study backed his conclusion.

The best-known attempt came 30 years after Stanford. In December 2001, Reicher, of the University of St Andrews, and Haslam, then of the University of Exeter, ran a study with 15 men in a mock prison built at Elstree film studios near London, filmed by BBC television. The BBC's advertisement warned volunteers of hardship, hunger, solitude and anger. An independent ethics committee monitored the study, and two clinical psychologists could remove any participant at any time. Before the programme was aired, Zimbardo said such research was now considered unethical and "should not be redone just for sensational TV".

The BBC guards never took to their role, and several were reluctant to use their authority. The researchers had told everyone that one prisoner could be promoted to guard. Once that promotion was made and no more were on offer, the prisoners began to act together, and on the sixth day they broke out of their cells and took over the guards' quarters. Guards and prisoners then agreed to run the place together as equals. That arrangement soon broke down, and four participants began pushing for a harsher prison with themselves as the guards. The study was stopped early, after eight or nine of a planned 10 days, amid concern for the participants' wellbeing, The Guardian reported at the time.

Reicher and Haslam concluded that "people do not automatically assume roles that are given to them". People are more willing to accept harsh, authoritarian rule, they argued, when their own group has failed and they feel powerless. They also argued that some of their guards held back because they knew a national television audience would later judge them. Zimbardo dismissed the BBC project as a "made-for-TV study" that could not count as a scientific repeat of his own.

Where the argument stands

In 2018, after years of public sparring, Zimbardo and Haney signed a joint statement with Reicher and Haslam. It called both the Stanford and BBC studies valid, and expressed regret for the personal attacks of earlier years. Two years later, Zimbardo and Haney wrote that the Stanford experiment had been intended as an exploratory demonstration, without the controls of a classic experiment. As a result, they wrote, there was no definitive way to tell whether the guards turned cruel because of the roles they were given or because the researchers led them there. Both, they said, were probably at work.

Critics and defenders of the experiment accept that prisoners in the Stanford basement went through real distress in August 1971. They still disagree over whether the prison turned the guards cruel, or the researchers who built it and told the guards what was expected of them.

Zimbardo died in October 2024, aged 91.