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In August of 1971, psychologistPhilip Zimbardoand his colleagues created an experiment to determine the impacts of being a prisoner or prison guard.The Stanford Prison Experiment, also known as the Zimbardo Prison Experiment, went on to become one of thebest-known studies in psychology’s history—and one of the most controversial.

This study has long been a staple in textbooks, articles, psychology classes, and even movies. Learn what it entailed, what was learned, and the criticisms that have called the experiment’s scientific merits and value into question.

Purpose of the Stanford Prison Experiment

Zimbardo was a former classmate of the psychologistStanley Milgram. Milgram is best known for his famousobedience experiment, and Zimbardo was interested in expanding upon Milgram’s research. He wanted to further investigate the impact of situational variables on human behavior.

Specifically, the researchers wanted to know how participants would react when placed in a simulated prison environment. They wondered if physically and psychologically healthy people who knew they were participating in an experiment would change their behavior in a prison-like setting.

Types of Variables in Psychology Research

Participants in the Stanford Prison Experiment

To carry out the experiment, researchers set up a mock prison in the basement of Stanford University’s psychology building. They then selected 24 undergraduate students to play the roles of both prisoners and guards.

Participants were chosen from a larger group of 70 volunteers based on having no criminal background, nopsychological issues, and no significant medical conditions. Each volunteer agreed to participate in the Stanford Prison Experiment for one to two weeks in exchange for $15 a day.

Setting and Procedures

The 24 volunteers were randomly assigned to either the prisoner or guard group. Prisoners were to remain in the mock prison 24 hours a day during the study. Guards were assigned to work in three-man teams for eight-hour shifts. After each shift, they were allowed to return to their homes until their next shift.

Researchers were able to observe the behavior of the prisoners and guards using hidden cameras and microphones.

Results of the Stanford Prison Experiment

So what happened in the Zimbardo experiment? While originally slated to last 14 days, it had to be stopped after just six due to what was happening to the student participants.The guards became abusive and the prisoners began to show signs ofextreme stress and anxiety.

It was noted that:

Even the researchers themselves began to lose sight of the reality of the situation. Zimbardo, who acted as the prison warden, overlooked the abusive behavior of the jail guards until graduate student Christina Maslach voiced objections to the conditions in the simulated prison and the morality of continuing the experiment.

One possible explanation for the results of this experiment is theidea of deindividuation, which states that being part of a large group can make us more likely to perform behaviors we would otherwise not do on our own.

The Mental Health Effects of Being in Prison

Impact of the Zimbardo Prison Experiment

The experiment became famous and was widely cited in textbooks and other publications. According to Zimbardo and his colleagues, the Stanford Prison Experiment demonstrated the powerful role that the situation can play in human behavior.

Because the guards were placed in a position of power, they began to behave in ways they would not usually act in their everyday lives or other situations. The prisoners, placed in a situation where theyhad no real control, became submissive and depressed.

In 2011, theStanford Alumni Magazinefeatured a retrospective of the Stanford Prison Experiment in honor of the experiment’s 40th anniversary. The article contained interviews with several people involved, including Zimbardo and other researchers as well as some of the participants.

In the interviews, Richard Yacco, one of the prisoners in the experiment, suggested that the experiment demonstrated the power that societal roles and expectations can play in a person’s behavior.

In 2015, the experiment became the topic of a feature film titledThe Stanford Prison Experimentthat dramatized the events of the 1971 study.

Criticisms of the Stanford Prison Experiment

In the years since the experiment was conducted, there have been a number of critiques of the study. Some of these include:

Ethical Issues

Why was Zimbardo’s experiment unethical?Zimbardo’s experiment was unethical due to a lack of fully informed consent, abuse of participants, and lack of appropriate debriefings. More recent findings suggest there were other significant ethical issues that compromise the experiment’s scientific standing, including the fact that experimenters may have encouraged abusive behaviors.

Why was Zimbardo’s experiment unethical?

Zimbardo’s experiment was unethical due to a lack of fully informed consent, abuse of participants, and lack of appropriate debriefings. More recent findings suggest there were other significant ethical issues that compromise the experiment’s scientific standing, including the fact that experimenters may have encouraged abusive behaviors.

Lack of Generalizability

Other critics suggest that the study lacks generalizability due to a variety of factors.Theunrepresentative sampleof participants (mostly white and middle-class males) makes it difficult to apply the results to a wider population.

Lack of Realism

The Zimbardo Prison Experiment is also criticized for its lack of ecological validity.Ecological validityrefers to the degree of realism with which a simulated experimental setup matches the real-world situation it seeks to emulate.

While the researchers did their best to recreate a prison setting, it is simply not possible to perfectly mimic all the environmental and situational variables of prison life. Because there may have been factors related to the setting and situation that influenced how the participants behaved, it may not truly represent what might happen outside of the lab.

Recent Criticisms

More recent examination of the experiment’s archives and interviews with participants have revealed major issues with theresearch method, design, and procedures used. Together, these call the study’s validity, value, and even authenticity into question.

These reports, including examinations of the study’s records and new interviews with participants, have also cast doubt on some of its key findings and assumptions.

Among the issues described:

In 2019, the journalAmerican Psychologistpublished an article debunking the famed experiment. It detailed the study’s lack of scientific merit and concluded that the Stanford Prison Experiment was “an incredibly flawed study that should have died an early death.”

In a statement posted on the experiment’s official website, Zimbardo maintains that these criticisms do not undermine the main conclusion of the study—that situational forces can alter individual actions both in positive and negative ways.

Takeaway

The Stanford Prison Experiment is well known both inside and outside thefield of psychology. While the study has long been criticized for many reasons, more recent criticisms of the study’s procedures shine a brighter light on the experiment’s scientific shortcomings.

Mental Health Effects Facing Recently Released Prisoners

11 SourcesVerywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Stanford University.About the Stanford Prison Experiment.Stanford Prison Experiment.2. Setting up.Sommers T.An interview with Philip Zimbardo.The Believer.Ratnesar R.The menace within.Stanford Magazine.Jabbar A, Muazzam A, Sadaqat S.An unveiling the ethical quandaries: A critical analysis of the Stanford Prison Experiment as a mirror of Pakistani society.J Bus Manage Res. 2024;3(1):629-638.Horn S.Landmark Stanford Prison Experiment criticized as a sham.Prison Legal News.Bartels JM.The Stanford Prison Experiment in introductory psychology textbooks: A content analysis.Psychol Learn Teach. 2015;14(1):36-50. doi:10.1177/1475725714568007American Psychological Association.Ecological validity.Blum B.The lifespan of a lie.Medium.Le Texier T.Debunking the Stanford Prison Experiment.Am Psychol. 2019;74(7):823-839. doi:10.1037/amp0000401Stanford Prison Experiment.Philip Zimbardo’s response to recent criticisms of the Stanford Prison Experiment.

11 Sources

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Stanford University.About the Stanford Prison Experiment.Stanford Prison Experiment.2. Setting up.Sommers T.An interview with Philip Zimbardo.The Believer.Ratnesar R.The menace within.Stanford Magazine.Jabbar A, Muazzam A, Sadaqat S.An unveiling the ethical quandaries: A critical analysis of the Stanford Prison Experiment as a mirror of Pakistani society.J Bus Manage Res. 2024;3(1):629-638.Horn S.Landmark Stanford Prison Experiment criticized as a sham.Prison Legal News.Bartels JM.The Stanford Prison Experiment in introductory psychology textbooks: A content analysis.Psychol Learn Teach. 2015;14(1):36-50. doi:10.1177/1475725714568007American Psychological Association.Ecological validity.Blum B.The lifespan of a lie.Medium.Le Texier T.Debunking the Stanford Prison Experiment.Am Psychol. 2019;74(7):823-839. doi:10.1037/amp0000401Stanford Prison Experiment.Philip Zimbardo’s response to recent criticisms of the Stanford Prison Experiment.

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Stanford University.About the Stanford Prison Experiment.Stanford Prison Experiment.2. Setting up.Sommers T.An interview with Philip Zimbardo.The Believer.Ratnesar R.The menace within.Stanford Magazine.Jabbar A, Muazzam A, Sadaqat S.An unveiling the ethical quandaries: A critical analysis of the Stanford Prison Experiment as a mirror of Pakistani society.J Bus Manage Res. 2024;3(1):629-638.Horn S.Landmark Stanford Prison Experiment criticized as a sham.Prison Legal News.Bartels JM.The Stanford Prison Experiment in introductory psychology textbooks: A content analysis.Psychol Learn Teach. 2015;14(1):36-50. doi:10.1177/1475725714568007American Psychological Association.Ecological validity.Blum B.The lifespan of a lie.Medium.Le Texier T.Debunking the Stanford Prison Experiment.Am Psychol. 2019;74(7):823-839. doi:10.1037/amp0000401Stanford Prison Experiment.Philip Zimbardo’s response to recent criticisms of the Stanford Prison Experiment.

Stanford University.About the Stanford Prison Experiment.

Stanford Prison Experiment.2. Setting up.

Sommers T.An interview with Philip Zimbardo.The Believer.

Ratnesar R.The menace within.Stanford Magazine.

Jabbar A, Muazzam A, Sadaqat S.An unveiling the ethical quandaries: A critical analysis of the Stanford Prison Experiment as a mirror of Pakistani society.J Bus Manage Res. 2024;3(1):629-638.

Horn S.Landmark Stanford Prison Experiment criticized as a sham.Prison Legal News.

Bartels JM.The Stanford Prison Experiment in introductory psychology textbooks: A content analysis.Psychol Learn Teach. 2015;14(1):36-50. doi:10.1177/1475725714568007

American Psychological Association.Ecological validity.

Blum B.The lifespan of a lie.Medium.

Le Texier T.Debunking the Stanford Prison Experiment.Am Psychol. 2019;74(7):823-839. doi:10.1037/amp0000401

Stanford Prison Experiment.Philip Zimbardo’s response to recent criticisms of the Stanford Prison Experiment.

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