The Stanford prison experiment tested what would happen when a group of subjects was pushed in the role of prisoner, while a second group was assigned the role of guards. Within merely a day or so, the guards started to harass the prisoners, humiliate them and made the prisoners physically and mentally suffer, forcing them to cleaning out toilet bowls with their bare hands, do push-ups, jumping jacks and what not.

Now I am wondering - how can normal people turn so evil? Were the assigned guards tested for any existing psychological problems prior to the experiment, or were they randomly chosen? In general, how did the researchers choose the subjects?

  • $\begingroup$ @adelrahimi, as the Gulag accounts (both the prisoners' and guards') show, when normal people are put in unimaginable conditions, they are capable of unimaginable lows - and highs. Often this happened with the people you'd least expect such things from. What makes it even more relevant is that psychologically at least, the guards were not that much different to the prisoners. As Dovlatov, who served as a guard, said, little would change if they swapped their roles. $\endgroup$
    – Zeus
    Commented Jul 11, 2016 at 1:47

1 Answer 1


The subjects in this experiment were randomly assigned in two groups (prisoner versus guard). They were all healthy and without any identified psychological issues. I quote from the Setting-Up page of your linked website:

We wanted to see what the psychological effects were of becoming a prisoner or prison guard. To do this, we decided to set up a simulated prison and then carefully note the effects of this institution on the behavior of all those within its walls.

More than 70 applicants answered our ad and were given diagnostic interviews and personality tests to eliminate candidates with psychological problems, medical disabilities, or a history of crime or drug abuse. Ultimately, we were left with a sample of 24 college students from the U.S. and Canada who happened to be in the Stanford area and wanted to earn $15/day by participating in a study. On all dimensions that we were able to test or observe, they reacted normally.

Our study of prison life began, then, with an average group of healthy, intelligent, middle-class males. These boys were arbitrarily divided into two groups by a flip of the coin. Half were randomly assigned to be guards, the other to be prisoners.

Note that people can do pretty nasty stuff under experimental conditions. For instance, take the Milgram experiment. In this experiment, actors were placed behind a closed door. They would be faking a test subject being electrocuted up until the point of agony. The real test subjects were instructed that they would be helping in an experiment where the effect of punishment through electric shocks would be tested in a learning task. The actors had to answer questions and when they were wrong, the test subjects were instructed to deliver increasingly stronger electrical shocks by pushing a button, until the trainee would improve their performance on the task. This experiment ended up with people consciously electrocuting innocent volunteers. Although everything was faked behind the scenes, it did show that regular, healthy test subjects obediently followed the instructions of the authorative experimenter when instructed to increase the voltage and electrocute the person behind the door, even when the actor was screaming in agony and explaining having a heart rhythm disorder.

Note that both the Milgram experiment and the Stanford study have been questioned because of lack of scientific rigor (Grigs, 2018; Texier, 2019).

- Grigs, Teaching Psychol (2017)); 44(1): 32-7
- Texier, Am Psychol (2019); 74(7): 823-39

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    $\begingroup$ This is a correct answer to the title question, but note that both the Stanford Prison and Milgram Experiment have been widely discredited, so we should not jump to any conclusions about how people would actually behave under such circumstances based on these studies alone. $\endgroup$
    – Arnon Weinberg
    Commented Jan 4, 2022 at 5:37
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    $\begingroup$ @ArnonWeinberg - I have added a concluding sentence on this, thanks, $\endgroup$
    – AliceD
    Commented Jan 4, 2022 at 8:55
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    $\begingroup$ They have been heavily criticised @ArnonWeinberg, but as stated after another comment you said this in, the criticism does not take anything away from the fact that some in the Milgram Experiment did take the conformity to deadly levels and the Stanford Prison Experiment was controversial because abuse was meted out which was not stopped until someone else intervened. Nevertheless, again, it showed how people can, and will, take things to extremes. $\endgroup$ Commented Jan 4, 2022 at 9:26
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    $\begingroup$ @ChrisRogers that's exactly what I was trying to say, yet you do it more clearly :) I have read a couple of recent reviews on this matter and they fully agree with your statements. But nonetheless I agree with Arnon that the criticisms deserve mention. $\endgroup$
    – AliceD
    Commented Jan 4, 2022 at 10:32
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    $\begingroup$ I also agree that the criticisms need a mention as they provide balance when taken into account within a "summary of findings". $\endgroup$ Commented Jan 4, 2022 at 10:37

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