Haney, Craig., Banks, Curtis., & Zimbardo, Philip. (1973)
A Study of Prisoners and Guards in a Simulated Prison.
study was funded by the US Navy, as it and the US Marine Corps were
interested in finding out the causes of conflict between guards and
prisoners in the naval prisons. Attempts to explain the violent and brutal conditions often
found in prisons had previously used dispositional attribution.
That is, that the state of the prison is due to the nature of
the prison guards and the prisoners.
example, it had been argued that prison guards bring to their jobs a
particular ‘guard mentality’ and are therefore attracted to the
job as they are already sadistic and insensitive people.
Whereas prisoners are individuals who have no respect for law
and order and bring this aggressiveness and impulsivity to the
Zimbardo was interested in testing this dispositional hypothesis by
demonstrating that the conditions of the prisons were not a result
of the type of individuals working and incarcerated in the prisons
and hoped to go on to help the Navy develop training, which would
eliminate the deplorable conditions in the prisons.
believed that the behaviour in prisons could be best explained using
a situational attribution. In
particular he believed that the conditions were influenced by the
social roles that prisoners and prisoner guards are expected to
put this quite well when he wrote ‘All the world’s a stage, and
all the men and women players’ (As You Like It).
Suggesting that we are what we play.
all play many roles in society and these social roles do to some
extent shape our identity. Each role we play brings with it certain rules or
expectations about how we should behave.
For example when we play the role of a student there may be
very different expectations about how we should behave compared with
say the role of an audience member at the Rocky Horror Picture Show. Similarly there may be certain expectations about the
role a prisoner or prison guard should play.
aim of the study was to investigate the effects of being assigned to
the role of either a prison guard or prisoner.
study is usually described as an experiment with the independent
variable being the conditions the participants are randomly
allocated to. Either
prisoner or guard. The
dependent variable is the resulting behaviour.
study can also be described as a simulation as it was attempting to
create a prison like environment.
collected were combinations of both quantitative and qualitative
data. The main data
though was qualitative and was obtained using video, audiotape and
participants were respondents to a newspaper advertisement, which
asked for male volunteers to participate in a psychological study of
‘prison life’ in return for payment of $15 per day.
75 respondents completed a questionnaire about their family
background, physical and mental health, prior experiences and
attitudinal tendencies with respect to psychopathology and any
involvement in crime.
on the results of the tests 24 men were selected.
These 24 were judged to be the most physically and mentally
stable, most mature, and least involved in antisocial behaviours.
The participants were described as “normal, healthy male
college students who were predominantly middle class and white.” The 24 participants did not know each other prior to the study.
simulated prison was built in the basement of the psychology
building at Stanford University. The simulated prison comprised of:
Three small cells
(each 6 x 9 ft) with three prisoners to a cell.
The cells contained three cots (with mattress, sheet and
pillow) for each prisoner.
was an extremely small, unlit room (2 x 2 x 7 ft).
This room was across from the cells.
Several rooms in
an adjacent wing of the building were used as guards’ quarters (to
change in and out of uniform and for relaxation), interview rooms
and a bedroom for the ‘warden’ and ‘superintendent’
A small, enclosed
room, which was used as a ‘prison yard’.
equipment was placed behind an observation screen
the duration of the study the prisoners remained in the mock prison
for 24 hours. Three
were arbitrarily assigned to each of the three cells, and the others
were on stand-by at their homes.
The guards worked on three-man eight-hour shifts, and went
home after their shifts.
participants all agreed voluntarily to play the role for $15 a day
for up to two weeks. The
participants signed a contract guaranteeing basic living needs, such
as an adequate diet and medical care. Although it was made explicit
in the contract that if they were to be assigned to the role of
prisoner they would have to have some basic civil rights (e.g.
The participants were not given any information about what to
expect and how to behave.
24 participants were randomly assigned to the role of ‘prisoner’
or ‘guard’ and informed by telephone to be available at their
homes on a particular Sunday when the experiment would begin.
participants allocated the role of guards had to attend an
orientation meeting the day before the induction of the prisoners.
They met the principal investigators, the
‘superintendent’ of the prison (Zimbardo) and the ‘warden’
(undergraduate research assistant).
They were told that the ‘experimenters wanted to try to
simulate a prison environment within the limits imposed by pragmatic
and ethical considerations’.
Their assigned task as prison guards was to ‘maintain
the reasonable degree of order within the prison necessary for
guards were instructed in their administrative details, including;
the work-shifts, the completion of ‘critical incident’ reports,
and the managing of meals, work and recreation programmes for the
prisoners. In order to
start involving the guards in their roles even before the prisoners
were incarcerated, they assisted in the final phases of completing
the prison complex – putting the cots in the cells, moving
furniture and so on. However
the guards were not told how to behave apart from being explicitly
told that they were not allowed to use physical punishment or
guards believed that the experimenters were mainly interested in
studying the behaviour of the prisoners although the experimenters
were just as interested in their behaviour.
uniforms of both prisoners and guards were intended to increase
group identity and reduce individuality within the two groups.
guards’ uniform consisted of a plain khaki shirt and trousers, a
whistle, a police night stick (a wooden batten) and reflecting
sunglasses, which made eye contact impossible.
The guards’ uniforms were intended to convey a military
attitude, while the baton and whistle were symbols of control and
prisoners’ uniform consisted of a loose-fitting muslin smock with
an identification number on the front and back, no underwear, rubber
sandals, a hat made from a nylon stocking and they had a light chain
and lock around their ankle. Each prisoner was also issued with a toothbrush, soap,
soap-dish, towel and bed linen.
No personal belongings were allowed in the cell. The
prisoners’ uniforms were designed to de-individuate the prisoners
and to be humiliating and serve as symbols of subservience and
dependence. The ankle
chain was a constant reminder of the oppressiveness of the
stocking cap removed any distinctiveness associated with hair
length, colour and style (as does shaving of heads in some
‘real’ prisons). The
ill-fitting uniforms made the prisoners feel awkward in their
movements; since these ‘dresses’ were worn without underwear,
the prisoners were forced to assume unfamiliar postures, more like
those of a woman than a man - another part of the emasculating
prisoner participants were unexpectedly ‘arrested at their homes
with the cooperation of the local police department.
A police officer then charged them with suspicion of burglary
or armed robbery, advised them of their rights, handcuffed them,
thoroughly searched them (often in full view of their neighbours and
passers by) and drove them in the back of a police car to the police
the police station they had their fingerprints and photograph taken
and were put in a detention cell.
Each prisoner was then blindfolded and driven to the mock
prison by one of the experimenters and a guard.
Throughout this arrest procedure, the police officers
involved maintained a formal, serious attitude, and did not tell the
participants that this had anything to do with the mock prison
the mock prison, each prisoner was stripped, sprayed with a
delousing preparation (a deodorant spray) and made to stand alone
and naked in the ‘yard’. After
being given their uniform and having a mug shot (ID picture) taken,
the prisoner was put in his cell and ordered to remain silent.
warden read them the rules of the institution (developed by the
guards and the warden), which were to be memorised and had to be
were to be referred to only by the number on their uniforms, also in
an effort to depersonalise them.
day the participants were allowed three bland meals, three
supervised toilet visits, and given two hours for the privilege of
reading or letter writing. Work
assignments had to be carried out and two visiting periods per week
were scheduled, as were movie rights and exercise periods.
Three times a day prisoners were lined up for a ‘count’ (one on each guard work-shift). The original purpose of the ‘count’ was to establish that all prisoners were present, and to test them on the knowledge of the rules and their ID numbers. The first ‘counts’ lasted only about ten minutes but as conditions in the prison deteriorated, they increased in length until some lasted for several hours.
summary the study showed that the behaviour of the ‘normal’
students who had been randomly allocated to each condition, was
affected by the role they had been assigned, to the extent that they
seemed to believe in their allocated positions.
The study therefore rejects the dispositional hypothesis.
The experiment had to be stopped after just
six days instead of the planned 14 days, mainly because of the
pathological reactions of the participants. Five
prisoners had to be released even earlier because of extreme
general, the guards and prisoners showed a marked tendency towards
increasingly negative emotions, and their overall outlook became
increasingly negative. Despite
the fact that guards and prisoners were essentially free to engage
in any form of interaction, the nature of their encounters tended to
be negative, hostile, insulting and dehumanising. The prison was internalised
by both the prisoners and the guards, that is, they started to
believe in it. They
adopted very contrasting behaviours, which were appropriate for
their respective roles. The
guards started most of the interactions, most of which were in the
form of commands or verbal affronts, while the prisoners adopted a
generally passive response mode.
Although it was clear to all participants that the
experimenters would not permit physical violence to take place,
varieties of less direct aggressive behaviour were often observed.
of the most dramatic evidence of the impact of this situation upon
the participants was when five prisoners had to be released early
due to extreme emotional depression, crying, rage and acute anxiety.
Of the remaining prisoners, only two said they were not
willing to forfeit the money they had earned in return for being
‘paroled’. When the
simulation was terminated after only six days instead of the
projected fourteen days all of the remaining prisoners were
delighted by the news, but most of the guards seemed to be
distressed by the premature end to the study - it appeared that they
had become sufficiently involved in their role that they now enjoyed
the extreme control and power which they exercised.
This is referred to by Zimbardo as pathology of power.
there were individual differences in styles of coping with this
novel experience. Half
of the prisoners endured the oppressive atmosphere, and not all the
guards resorted to hostility, some guards were tough but fair, while
some went far beyond their roles to engage in creative cruelty and
believes that the study demonstrate the powerful effect roles can
have on peoples’ behaviour. Basically
the participants were playing the role that they thought was
expected of, either a prisoner or prison guard. (It is in fact a simulation of what we expect prison life
to be, rather than what it is, as none of the participants had
previously been in prison as a guard or prisoner).
then went on to explain the prison guards’ behaviour and the
explains that the reason for the deterioration in guard behaviour
The guards were given control over the lives of other human
beings and did not have to justify their displays of power as they
would normally have to in their daily lives.
They started to enjoy this power very earlier on in the study
(pathology of power) as demonstrated that even after the first day
all prisoner rights became redefined as privileges, and all
privileges were cancelled.
explains the social deterioration of the prisoners as the pathological
At the beginning of the study, the prisoners rebelled against
their conditions, but the guards undermined every attempt at
rebellion, and any solidarity between the prisoners collapsed.
Half of the prisoners responded by becoming sick, and
eventually had to be released before the study was finally brought
to a conclusion. The
remaining prisoners became passive, dependent and had flattened
suggested that there were a number of processes that contributed to
the pathological prisoner syndrome:
loss of personal identity
– the prisoners were de-individuated by being stripped of their
individuality, their name, dress, appearance, behaviour style, and
history. Living among
strangers who do not know your name or history, dressed like all the
other prisoners, all led to the weakening of self-identity among the
prisoners became de-individuated not only to the guards, but to
arbitrary control exercised by the guards
- on post-experimental questionnaires, the prisoners said they
disliked the way that the way they were subjected to the arbitrary
and changeable decisions and rules of the guards as this made life
unpredictable and unfair. For example, smiling at a joke could be punished in the
same way that failing to smile might be.
As the environment became more unpredictable, the
prisoners’ behaviour showed signs of learned
helplessness, that is, as the prisoners’ previously learned
assumptions about a just and orderly world were no longer
functional, they ceased to initiate any action;
· Dependency and emasculation - the prisoners were made to be totally dependent on the guards for commonplace functions such as going to the toilet, reading, lighting a cigarette and this emasculated them. The smocks, worn without underwear, lessened their sense of masculinity. This was taken to the extent that when the prisoners were debriefed they suggested that they had been assigned to be prisoners because they were smaller than the guards. In fact there was no difference in average height between the prisoners and guards, and the perceived difference was a response to the prisoners’ perception of themselves and their lack of power.
main criticism of Zimbardo’s study is on ethical grounds.
Zimbardo does defends the experiment in a number of ways:
involved was to do with the arrest of the prisoners at the beginning
of the experiment. The
prisoners were not told partly because final approval from the
police wasn’t given until minutes before the participants decided
to participate, and partly because the researchers wanted the
arrests to come as a surprise.
However this was a breach of the ethics of Zimbardo’s own
contract that all of the participants had signed.
Zimbardo realised just how much the prisoners disliked the
experience, which was unexpected, the experiment was abandoned.
for the study was given from the Office of Naval Research, the
Psychology Department and the University Committee of Human
Experimentation. This Committee also did not anticipate the prisoners
extreme reactions that were to follow.
methodologies were looked at which would cause less distress to the
participants but at the same time give the desired information, but
nothing suitable could be found.
group and individual debriefing
sessions were held and all participants returned post-experimental
questionnaires several weeks, then several months later, then at
also strongly argues that the benefits gained about our
understanding of human behaviour and how we can improve society
should out balance the distress caused by the study.
However it has been suggested that the US Navy was not so
much interested in making prisons more human and were in fact more
interested in using the study to train people in the armed services
to cope with the stresses of captivity.
study can also be criticised for its unrepresentative sample.
Since the experiment was conducted using 24 normal, healthy, male
college students who were predominantly middle class and white (one
was described as oriental), we have to be careful generalising the
results to other people.
the study has been criticised for lacking ecological validity.
For practical and ethical reasons the simulated prison could
not be totally realistic. Many
particularly unpleasant aspects of prison life were absent, such as
involuntary homosexuality, racism, beatings and threats to life.
Also, the maximum anticipated sentence was just two weeks.
It is therefore possible that the study does not serve as a
meaningful comparison to real prison environments.
However, there is considerable evidence that the participants
did react to the situation as though it was real.
For example 90% of the prisoners’ private conversations,
which were monitored by the researchers, were on the prison
conditions, and only 10% of the time were their conversations about
life outside of the prison. The
guards, too, rarely exchanged personal information during their
relaxation breaks - they either talked about ‘problem
prisoners’, other prison topics, or did not talk at all.
The guards were always on time and even worked overtime for
no extra pay. When the
prisoners were introduced to a priest, they referred to themselves
by their prison number, rather than their first name.
Some even asked him to get a lawyer to help get them out.
main strength of the study was the way it managed to maintain some
degree of control and some ecological validity.
The situation was very tightly controlled e.g. guards and
prisoners were randomly allocated and were selected using a
stringent criterion. The
study still had ecological validity in the way that Zimbardo went to
great extremes in making the study as true to life as possible, for
example in the way that he had the prisoners arrested from their
A further strength was in the way that Zimbardo collected data. He used a number of qualitative approaches such as observation (sometimes overt and sometimes covert) interviews and questionnaires.
study was clearly trying to give a situational explanation for
argued that the study demonstrates the powerful effect roles can have on
some psychologists believe that he has over emphasised the
situational explanation. They
state that the behaviour of both prisoners and guards may have
arisen from the stereotyped expectations of how prisoners and guards
should behave. That is,
the participants were only role-playing.
However, Zimbardo would strongly suggest that the
participants’ experiences were all too real and that even if they
were only role-playing at the beginning of the study, as the study
progressed they were internalising these roles and they could no
longer differentiate between role-playing and self.
is also worth noting that Zimbardo’s argument can be seen
as too deterministic. For
example in Zimbardo’s study not all of the participants behaved in
the same way. For
example, some of the guards were less willing to abuse their power.
Perhaps the reason why some of the participants were less
willing was something to do with their personalities.
Haney, C., Banks, W.C. & Zimbardo, P.G. (1973) A study of prisoners and guards in a simulated prison. Naval Research Review, 30, 4-17.
GROSS, R. (1999) Key Studies in Psychology, 3rd Edition. London: Hodder and Stoughton
BANYARD, P. AND GRAYSON, A. (2000) Introducing Psychological Research; Seventy Studies that Shape Psychology, 2nd Edition. London: Macmillan
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