Analysis of “A Study of Prisoners and Guards in a Simulated Prison”

Analysis of “A Study of Prisoners and Guards in a Simulated Prison”

Criticism of the Stanford Prison Experiment


One of the most famous tests ever conducted, the Stanford Prison Test, formally known as “A Study of Prisoners and Guards in a Simulated Prison” was conducted by Philip Zimbardo, Craig Haney, and Curtis Banks at Stanford University. This study is one of the most cited tests despite being ended early for safety and ethical reasons. The hypothesis of the experiment seemed to be proven in light of these issues and as a result has become an academic point of reference when discussing prison violence and its causes. An analysis of the Stanford Prison Experiment reveals flaws, which should be considered along with the outcomes of this study.

Background and Purpose

The Stanford Prison Experiment was conceived by Philip Zimbardo who wanted to see the impact of the prison environment on inmates and guards. Within this framework, “No specific hypotheses were advanced other than the general one that assignment to the treatment of “guard” or “prisoner” would result in significantly different reactions on behavioral measures of interaction, emotional measures of mood state and pathology, attitudes toward self, as well as other indices of coping and adaptation to this novel situation” (Haney, Banks , & Zimbardo, 1973). The specific intent of the research was to show whether prison roles would causes changes in psychology.

Study Design and Methodology

The research was designed as a simulated prison environment that used single treatment variable of role designation with participants being assigned “guard” or “prisoner”. The idea behind this design was to create an approximation of real prison conditions where each role was provided different directives. Guards were directed to maintain order without using physical violence or certain forms of psychological abuse such as racism or other overt forms of abuse. Prisoners were directed to mimic a real prison environment by having to do things such as asking to use the bathroom send mail. The roles were operationally defined as:

The “prisoner” subjects remained in the mock-prison 24 hours per day for the duration of the study. Three were arbitrarily assigned to each of the three cells; the others were on stand-by call at their homes. The “guard” subjects worked on three-man, eight-hour shifts; remaining in the prison environment only during their work shift and going about their usual lives at other times (Haney, Banks , & Zimbardo, 1973).

The study was designed to be observational in nature with researchers recording behavior using cameras (hidden and in plain sight) and journals. The research was a combination of qualitative and quantitative approaches that attempted to measure changes in behavior. The variables of the experiment were important to this study due to the need for randomization of the population. The independent variable was the random assignment of participants to the role of prison guards or prisoners. This random placement was defined as the ‘single treatment variable’ which identifies the singular roles and their conditions within the experiment. The dependent variable was the effect or measured impact of the interaction between independent variables. This created qualitative and quantitative results as behavioral changes could be both identified and recorded throughout the experiment.

Population and Sample

The population was intended to represent a prison environment or a general population of people. The sample size was 24 people with 22 participating subjects and was acquired from a newspaper ad asking for male volunteers who would be paid $15 per day (Haney, Banks , & Zimbardo, 1973). It was only possible to obtain 24 participants due to difficulties with the extensive questionnaire that has stringent requirements for, “family background, physical and mental health history, prior experience and attitudinal propensities with respect to sources of psychopathology (including their involvements in crime)” (Haney, Banks , & Zimbardo, 1973). Of the 24 chosen, 22 participated in the study with the remaining two as alternative participants.


The results of the study were taken from data collected after the experiment was terminated at the six-day mark. With the data collected from this period the findings were as follows:

*approximately 30% of the guards as ‘cruel and tough’; about 50% were ‘tough but fair’; *and less than 20% were ‘good guards’ (generally helpful and kind to the prisoners) (Haney, Banks , & Zimbardo, 1973). *Prisoners were depressed and were 90% focused on the prison conditions.

Researchers concluded that power was found to be the overarching factor that caused behavioral changes.


The Stanford Prison Experiment shows clearly that something occurs in prison settings but its findings are troublesome due to several factors which make the conclusions difficult to prove. The most troublesome part of the study is the population. The population that the test was intended to mimic was not indicative of prisons since the experiment used college students and significant differences can be seen in prison populations and college populations. To make this test more realistic a different population would need to be used that more closely represented the demographics of prison inmates.

The experiment also lacked a control group. Without some form of control group there is no way to tell if the behaviors were being caused by some other issue such as the design of the experiment itself. The groups were also too small of a sample, which creates validity issues. A sample size of 22 people is too small to create statistical significance in a group the size of a prison. There were also numerous validity problems in the study such as the ratio of guards to prisoners, lack of violence, the simulated or artificial nature of the environment, and the knowledge that a person could leave when they so desired.

A final issue with the experiment was the numerous ethical issues that were attached to the experiment. Besides the treatment of participants there was the issue of cameras being hidden as well as the over involvement of researchers in the experiment itself. The ethical issues present problems rendering the experiment unreplicable. This is extremely problematic because the methods themselves may be the cause of the changes in behavior.


While the researchers proved their hypothesis, this was only accomplished with the context of the experiment. The study in many ways was not realistic and because it cannot be replicated due to ethical reasons, it remains unchallenged, drawing into question the research conclusions. The researchers conclude power as the cause of behavioral changes which is expressed in the study:

The use of power was self-aggrandizing and self-perpetuating. The guard power, derived initially from an arbitrary and randomly assigned label, was intensified whenever there was any perceived threat by the prisoners and this new level subsequently became the baseline from which further hostility and harassment would begin. The most hostile guards on each shift moved spontaneously into the leadership roles of giving orders and deciding on punishments. They became role models whose behavior was emulated by other members of the shift (Haney, Banks , & Zimbardo, 1973).

Although power is a likely candidate for the behavioral changes in the study, this presents a very limited view of psychology. The limitations of the experiment preclude other causes such as characteristics that are unique to prisons such as gangs, overt racism, and other factors which may cause violent behavior and depression. More importantly, the design of the study itself may have created the behavioral changes in the participants due to the types of directives given, setting, and other contextual factors. It is highly likely that other more complicated factors were at work in the experiment. However, it is unlikely that this study will be challenged outside of criticism and debate due to the inability to replicate. More robust studies of prison environments need to be constructed but this remains a challenge due to the nature of prisons and the inability to safely observe these environments.


Haney, C., Banks , C., & Zimbardo, P. (1973, September). A Study of Prisoners and Guards in a Simulated Prison. Naval Research Reviews, 1–17. 

Photo by Guido Coppa on Unsplash

Updated: 10/07/2021


Triola Vincent. Fri, Jan 08, 2021. Analysis of “A Study of Prisoners and Guards in a Simulated Prison” Retrieved from

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