The Stanford Prison Experiment
An Experiment in
• On a quiet Sunday morning in
August, a police car swept
through the town picking up
college students as part of a
mass arrest for armed robbery
• The suspects were picked up at
their home, charged, spread-
eagled against the police car,
searched, and handcuffed.
Booking and Holding Cells
• The car arrived at the police station, the suspects were
brought inside, formally booked, read their Miranda Rights,
finger printed, and a complete identification was made.
▫ The suspects were then taken to a holding cell where they were
left blindfolded for as long as two hours.
Volunteering for the Experiment
• College students answered a newspaper ad asking for volunteers in a
study of the psychological effects of prison life, in an experiment
designed by Philip Zimbardo, a Stanford psychology professor.
• More than 70 applicants answered the ad and were given diagnostic
interviews and personality tests to eliminate candidates with
psychological problems, medical disabilities, or a history of crime.
▫ 24 college students from the U.S. and Canada who happened to be in the
Stanford area were selected and set to earn $15/day.
Constructing the Experiment
• The prison was constructed by boarding up each end of a
corridor in the basement of Stanford's Psychology Department
▫ That corridor was "The Yard" and was the only place where
prisoners were allowed to walk around, eat, or exercise.
▫ Cells were made from laboratory rooms with specially made
doors with steel bars and cell numbers.
• Each prisoner was systematically searched and stripped
naked. He was then deloused with a spray, to convey the
belief that they may have germs or lice.
• The prisoner was then issued a uniform. The main part of this
uniform was a dress, or smock, which each prisoner wore at
all times with no underclothes.
• On the smock, in front and in back, was his prison ID number.
• On each prisoner's right ankle was a heavy chain, bolted on
and worn at all times.
Becoming a Prisoner
• The chain on their foot was used in order to remind prisoners
of the oppressiveness of their environment.
▫ When a prisoner turned over, the chain would hit his leg, waking
him up and reminding him that he was still in prison.
• The process of having one's head shaved is designed in part to
minimize each person's individuality. It is also a way of getting
people to begin complying with the arbitrary, coercive rules of
Enforcing the Law
• The guards were free, within limits, to do whatever they thought was
necessary to maintain law and order in the prison.
▫ The guards made their own set of rules.
• All guards were dressed in identical uniforms of khaki, and wore a
whistle around their neck and a Billy club borrowed from the police.
▫ Guards also wore mirror sunglasses which prevented anyone from seeing
their eyes or reading their emotions.
In the Cells
• The experiment began with nine guards and nine prisoners in
the jail. Three guards worked each of three eight-hour shifts,
while three prisoners occupied each of the three barren cells
around the clock.
• The cells were so small that there was room for only three cots
on which the prisoners slept or sat, with room for little else.
• At 2:30 A.M. prisoners were awakened from sleep by blasting
whistles for the first of many "counts." The counts served as a
way to familiarizing the prisoners with their numbers.
▫ More importantly, they provided a regular occasion for the
guards to exercise control over the prisoners.
• Push-ups were a common form of physical punishment
imposed by the guards, for infractions of the rules or displays
of improper attitudes toward the guards or institution.
• One of the guards stepped on the prisoners' backs while they
did push-ups, or made other prisoners sit on the backs of
fellow prisoners doing their push-ups.
• Because the first day passed without incident, the guards were
surprised and totally unprepared for the rebellion which broke
out on the morning of the second day.
▫ Prisoners removed their stocking caps, ripped off their numbers,
and barricaded themselves inside the cells by putting their beds
against the door
• The guards were angered and frustrated because the prisoners
began to taunt and curse them. When the morning shift of
guards came on, they became upset at the night shift who,
they felt, must have been too lenient.
Putting Down the Rebellion
• The guards called in reinforcements. The three guards who
were waiting on stand-by duty came in and the night shift of
guards voluntarily remained on duty.
• The guards broke into each cell, stripped the prisoners naked,
took the beds out, forced the ringleaders of the prisoner
rebellion into solitary confinement.
• One of the three cells was designated as a
"privilege cell." The three prisoners least
involved in the rebellion were given special
▫ Given back their uniforms and beds and
were allowed to wash and brush their teeth.
• Privileged prisoners also got to eat special
food in the presence of the other prisoners
who had temporarily lost the privilege of
▫ The effect was to break the solidarity among
Consequences of Rebellion
• The prisoners' rebellion played an
important role in producing
greater solidarity among the
• It was no longer just an
• Now guards saw the prisoners as
troublemakers who were out to
get them, who might really cause
them some harm.
• In response to this threat, the
guards began increasing their
control, surveillance, and
• Less than 36 hours into the experiment,
Prisoner #8612 began suffering from acute
emotional disturbance, disorganized thinking,
uncontrollable crying and rage.
• After a meeting with the guards where they
told him he was weak, but offered him
“informant” status, #8612 returned to the
other prisoners and said “You can't leave. You
• Soon #8612 “began to act ‘crazy,’ to scream, to
curse, to go into a rage that seemed out of
▫ It wasn’t until this point that the psychologists
realized they had to let him out.
A Visit from Parents
• The next day, they held a visiting hour for parents and friends.
They were worried that when the parents saw the state of they
jail, they might insist on taking their sons home.
▫ Guards washed the prisoners, had them clean and polish their
cells, fed them a big dinner and played music on the intercom.
Stepping Things Up
• After the visit, rumor spread of a mass escape plan.
Afraid that they would lose the prisoners, the
guards and experimenters tried to enlist the help
and facilities of the Palo Alto police department.
• The guards again escalated the level of harassment,
forcing them to do menial, repetitive work such as
cleaning toilets with their bare hands.
An Informant in the Prison
• The guards had become so immersed in the
simulation they started getting paranoid. In an
attempt to stop further “plots,” the guards
planted an informant within the prison.
Falling Further From Reality
• Zimbardo invited a Catholic
priest who had been a prison
chaplain to evaluate how
realistic our prison situation
• The chaplain interviewed each
• The priest told them the only
way they would get out was
with the help if a lawyer.
Half the prisoners introduced
themselves by number rather
• The only prisoner who did not want to speak to the priest was
Prisoner #819, who was feeling sick, had refused to eat, and
wanted to see a doctor rather than a priest.
• Eventually while talking to the priest, #819 broke down and
began to cry hysterically, just as had the other two boys
• The psychologists removed the chain off his foot, the cap off
his head, and told him to go and rest in a room that was
adjacent to the prison yard. They told him they would get him
some food and then take him to see a doctor.
• While this was going on, one of the
guards lined up the other prisoners and
had them chant aloud:
• "Prisoner #819 is a bad prisoner.
Because of what Prisoner #819 did, my
cell is a mess, Mr. Correctional
• The psychologists realized #819 could
hear the chanting and went back into
the room where they found him sobbing
• The psychologists tried to get him to
agree to leave the experiment, but he
said he could not leave because the
others had labeled him a bad prisoner.
Back to Reality
• At that point, Zimbardo said, "Listen, you are not #819. You
are [his name], and my name is Dr. Zimbardo. I am a
psychologist, not a prison superintendent, and this is not a
real prison. This is just an experiment, and those are
students, not prisoners, just like you. Let's go."
• He stopped crying suddenly, looked up and replied, "Okay,
let's go,“ as if nothing had been wrong.
An End to the Experiment
• Christina Maslach, a recent Stanford Ph.D. brought in to
conduct interviews with the guards and prisoners, strongly
objected when she saw our prisoners being treated so poorly.
▫ Out of 50 or more outsiders who had seen our prison, she was the
only one who ever questioned its morality.
• Once she countered the power of the situation, however, it
became clear that the study should be ended.
Maslach was dating
Zimbardo at the time. They
are still married to this day.
In the End
• “By the end of the study, the prisoners were disintegrated,
both as a group and as individuals. There was no longer any
group unity; just a bunch of isolated individuals hanging on,
much like prisoners of war or hospitalized mental patients.
The guards had won total control of the prison, and they
commanded the blind obedience of each prisoner.”
The End of the Experiment
• After only six days, the planned two-week prison
simulation was called off.
• Do we see similarities to present day?
• What are the effects of living in an environment with no
clocks, no view of the outside world, and minimal sensory
• Consider the psychological consequences of stripping,
delousing, and shaving the heads of prisoners or members of
the military. What transformations take place when people go
through an experience like this?
• After the study, how do you think the prisoners and guards
• If you were the experimenter in charge, would you have done
this study? Would you have terminated it earlier? Would you
have conducted a follow-up study?