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Philip Zimbardo, psychologist who created the infamous 1971 Stanford Prison Experiment

Intended to run for two weeks, the study was halted after six days because, Zimbardo admitted, ‘it was out of control’

Philip Zimbardo, who has died aged 91, was a psychologist whose studies included work on shyness, the psychological roots of evil and the effects of the past on decision-making; but he was best known for the 1971 Stanford Prison Experiment, which was infamously abandoned after only six days.
Zimbardo’s study continued the work in the 1960s of the Yale social psychologist Stanley Milgram, who had tested subjects’ obedience to authority by having them deliver what they believed were electric shocks to “learners” in another room. He found that many of the subjects were willing to follow orders and deliver “shocks” at what would be lethal levels.
The Stanford Prison Experiment was designed to simulate a prison environment; 24 students at Stanford University in California were recruited for what was billed as a “psychological study of prison life” and offered $15 a day (worth about $116, or £89, today). They were assessed for their psychological stability and then, on the toss of a coin, assigned to be either prisoners or warders.
The “warders” were given uniforms and intimidating mirrored sunglasses – an idea Zimbardo adopted from the Paul Newman prison drama Cool Hand Luke – and told it was their job to prevent the “prisoners” escaping from the simulated jail in the basement of Stanford’s psychology department. They were told not to harm the prisoners but to maintain order.
The prisoners were given a strict regime and were dehumanised by being made to wear prison smocks, nylon stocking caps (in lieu of shaven heads) and no underwear. They were referred to by number and had to refer to the guards as “Mr Correctional Officer”.
As early as the second day the prisoners staged a revolt, which led the guards to turn fire hoses on them and demand as punishment that they either embrace or insult one another, strip naked or clean toilet bowls with their bare hands.
There was a visiting day for friends and family, and the prisoners were ordered to tell them that “everything is wonderful, hunky dory. If you don’t, we’re going to make things worse for you when they leave.”
As Zimbardo recalled, “Within 36 hours, the first normal, healthy student prisoner had a breakdown. We released a prisoner each day for the next five days.” When a fellow psychologist, Christina Maslach, came to inspect the project, she was so disturbed by what she saw that she convinced Zimbardo to call a halt. “We ended the experiment at six days because it was out of control,” he said. “There was no way to control the guards.”
There were abundant criticisms of the study: it was unscientific and unethical; there was no control group; the sample size of 24 was far too small to extrapolate anything meaningful; psychological distress was inflicted on subjects; and there was no oversight of the guards.
The Stanford Prison Experiment would not take place in the same form today: vulnerable participants would not be subject to psychological manipulation; it would be forbidden to encourage aggression and abuse between subjects; and the dramatic and uncontrolled nature of the study alone would make it a non-starter. Zimbardo defended his study, however, as “a cautionary tale”.
Philip George Zimbardo was born on March 23 1933 in New York into an impoverished family of Sicilian immigrants and grew up in South Bronx, where he was bullied for his foreign roots (his skin colour led people to believe that he was from Latin America). His father George had been a barber, like his father before him, then retrained as an electrician during the Second World War, but was frequently unemployed; Philip’s mother was Margaret, and he had two brothers and a sister.
He was a poorly child, spending long periods in hospital with recurrent pneumonia and asthma attacks, but in his teens he took a string of jobs to help the family finances – shining shoes, selling magazines door-to-door and delivering laundry.
He recalled finding inspiration in the life of Theodore Roosevelt, the US president who had overcome his sickly childhood with a robust exercise regime, and in his teens young Zimbardo embarked on a programme of hiking and sports to build himself up.
He graduated from Brooklyn College in 1954 in psychology, sociology and anthropology, going on to receive a masters and, from Yale, a doctorate. After a few years teaching at New York University and Columbia University, he joined Stanford in 1968, staying there until his retirement in 2003.
In the decades after the Experiment, Zimbardo’s work included founding a clinic to help those suffering from extreme shyness.
Though the Stanford experiment had been brought to an early end, Zimbardo drew upon it years later when he sought to explain the behaviour of US soldiers at Abu Ghraib prison following the 2003 invasion of Iraq, when detainees were subjected to torture and systematic humiliation.
General Richard Myers, chairman of the Joint Chiefs of Staff, blamed the abuses on “bad apples”. But Zimbardo insisted that it was the inhumane conditions at the prison that led to the soldiers’ behaviour, and he appeared as an expert witness on behalf of Staff Sgt Ivan “Chip” Frederick, who went on to serve half of an eight-year sentence for allowing and inflicting abuse.
“The military created a situation and then absolved themselves of any responsibility,” Zimbardo said later. “It’s not the grunts who should be punished. It’s the entire chain of command which has to be called to question.”
In 2007 he wrote The Lucifer Effect: Understanding How Good People Turn Evil, which contained the first detailed account of the Stanford Prison Experiment; reviewers tended to agree that it could not, strictly speaking, be called an “experiment”. The book’s transcripts formed the basis of the script for the 2015 feature film The Stanford Prison Experiment.
Philip Zimbardo married, first, Rose Abdelnour. They divorced, and in 1972 he married Christina Maslach, the psychologist who had persuaded him to end the Stanford study. She survives him with their two daughters and a son from his first marriage.
Philip Zimbardo, born March 23 1933, died October 14 2024

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