Philip Zimbardo defends the Stanford Prison Experiment, his most famous work

For decades, the story of the famous Stanford Prison Experiment has gone like this: Stanford professor Philip Zimbardo assigned paid volunteers to be either inmates or guards in a simulated prison in the basement of the school‘s psychology building. Very quickly, the guards became cruel, and the prisoners more submissive and depressed. The situation grew chaotic, and the experiment, meant to last two weeks, had to be ended after five days.

The lesson drawn from the research was that situations can bring out the worst in people. That, in the absence of firm instructions of how to act, we’ll act in accordance to the roles we’re assigned. The tale, which was made into a feature film, has been a lens through which we can understand human-rights violations, like American soldier’s maltreatment of inmates at the Abu Ghraib in Iraq in the early 2000s.

This month, the scientific validity of the experiment was boldly challenged. In a thoroughly reported exposé on Medium, journalist Ben Blum found compelling evidence that the experiment wasn’t as naturalistic and un-manipulated by the experimenters as we’ve been told.

A recording from the experiment reveals that the “warden,” a research assistant, told a reluctant guard that “the guards have to know that every guard is going to be what we call a ‘tough guard.’” The warden implored the guard to act tough because “we hope will come out of the study is a very serious recommendation for [criminal justice] reform.” The implication being that if the guard didn’t play the part, the study would fail.

Additionally, one of the “prisoners” in the study told Blum that he was “acting” during a what was observed to be a mental breakdown.

These new findings don’t mean that everything that happened in the experiment was theater. The “prisoners” really did rebel at one point, and the “guards” were cruel. But the new evidence suggests that the main conclusion of the experiment — the one that has been republished in psychology textbooks for years — doesn’t necessarily hold up. Zimbardo stated over and over the behavior seen in the experiment was the result of their own minds conforming to a situation. The new evidence suggests there was a lot more going on.

I wrote a piece highlighting Blum’s exposé and putting the prison experiment in the larger context of psychology’s replication crisis. Our headline stated “we just learned it [the Stanford Prison Experiment] was a fraud.”

Fraud is a moral judgment. And Zimbardo, now a professor emeritus, wrote to Vox, unhappy with this characterization of his study. (You can Zimbardo’s full written response to the criticisms here.)

So I called Zimbardo up to ask about the evidence in Blum’s piece. I also wanted to know: As a scientist, what do you do when the narrative of your most famous work changes dramatically and spirals out of your own control?

The conversation was tense. At one point, Zimbardo threatened to hang up.

Zimbardo believes Blum (and Vox) got the story wrong. He says only one guard was prodded to act tougher. (We did not discuss Blum’s evidence that the “prisoners” in the experiment were held against their will, despite pleas to leave.)

After talking with him, the results of the prison experiment still seem unscientific and untrustworthy. It’s an interesting demonstration, but should enduring lessons in psychology be based off of it? I doubt it.

Here’s our conversation, which has been edited for length and clarity.

Brian Resnick

Here’s my understanding of the criticisms that have come to light recently about the Stanford Prison Experiment.

For years, the conclusion that has been drawn from the study was that circumstances can bring out the worst in people or encourage bad behavior. And when some people are given power, and some people are stripped of it, that fosters ugly behavior.

What’s comes to light — what I got out of that Ben Blum’s report — was that it might not have all been the circumstance. That these guards that you employed were possibly coached in some ways.

There’s audio. And for me, it sounded pretty compelling that the warden in your experiment, who I understand was an experimental collaborator — was calling out a guard for not being tough enough. [The warden told the guard, “The guards have to know that every guard is going to be what we call a ‘tough guard.’” Listen to the tape here.]

So does that not invalidate the conclusion?

Philip Zimbardo

Not at all!

Brian Resnick

And why not?

Philip Zimbardo

Because he’s talking to one guard who was doing nothing. These are people we’ve hired who are doing it for a salary, $15 a day, to play the role of guard. And Jaffe [the warden] picks on this guy because he is doing nothing. He’s sitting on the sideline, doing nothing, watching. He’s gotta earn his keep as a guard.

The point is telling a guard to be tough does not mean telling a guard to be mean, to be cruel, to be sadistic, which many of the guards became of their own volition playing the role of what they thought was a prison guard. So I reject your assumption entirely.

Brian Resnick

Here’s the description of the experiment as written on your website: It says “the guards made up their own set of rules which they carried into effect.” In another paper, you wrote that the guards’ behavior was left up “to each subject’s prior societal learning of the meaning of prisons.”

But here’s a different possibility: Do you think it is possible that some of these guards were acting to please you, to please the study, and to do something good for science?

Even without telling the guards to explicitly do something, they might have gotten the impression that it was important for them to play these roles. And they were compelled to because of your authority.

Philip Zimbardo

Some of them might, but I think most of them didn’t.

For many of them, it was simply a way to make $15 a day during a two-week summer break between summer school and the start of classes in September. It was nothing more than that. It was not wanting to help science.

Some of them were increasingly mean, cruel, and sadistic way beyond any definition of tough. Some of them were guards who simply enforced the rules. And some of them were “good guards” who never did anything abusive to the prisoners. So it’s not that the situation brought a single quality in the guard. It’s a mix.

The criticism that you’re raising, that Blum raised, that others are raising, is that we told the guards to do what they ended up doing. And therefore, [the results were due to] obedience to authority, and it’s not the evolution of cruel behavior in the situation of a prison-like environment.

And I reject that.

Brian Resnick

Is it possible that some of the “prisoners” in your experiment were acting, playing along?

Philip Zimbardo

No, zero.

Brian Resnick

Zero? How can you say zero?

Philip Zimbardo

Okay, I can’t say.

I mean, the point was they locked themselves in their cells, they ripped off their numbers, they’re yelling and cursing at the guards. So, yeah, they could be acting. But why would they be acting. … What would they get out of that?

Brian Resnick

Blum quoted one of the prisoners, Douglas Korpi, who had a breakdown. Korpi told Blum that he was acting. That he was in the midsts of studying for the GREs and just really wanted to get out of the experiment. Korpi told Blum, “Anybody who is a clinician would know that I was faking.”

Philip Zimbardo

Brian, Brian, I’m telling you every fucking thing that Ben Blum said is a lie; it’s false.

Nothing Korpi said to Ben Blum has any truth, zero. Look at Quiet Rage [a documentary about the prison experiment], look at where he says, “I was overcome in that situation. I broke down, I lost control of myself.”

Retrospectively now, he’s ashamed of having broken down. So he says he “was studying the Graduate Record Exam, I was faking it, I wanted to show I could get out and liberate my colleagues,” etc, etc.

So he is the least reliable source of any information about the study, except he documents the power of the situation to get somebody who’s psychologically normal, 36 hours before, who in an experiment, knowing it’s an experiment, has an emotional “breakdown,” and had to be released.

Brian Resnick

Let’s say: Regardless of whether guards were coached or not…

Philip Zimbardo

Brian, I’m gonna stop you.

Brian Resnick

Can I finish the question?

Philip Zimbardo

A guard, a single guard, okay? When you say guards you’re slipping back into your assumption, you’re slipping back to be like Blum. A guard was coached to be tough, and end of sentence there.

[Note: As a reminder, the tape of the experiment quoted the Jaffe, the “warden,” who played a critical role in leading the experiment, as saying, “The guards have to know that every guard is going to be what we call a ‘tough guard.’” Also, as Blum discovered in the Stanford archives, Jaffe wrote in his notes, “I was given the responsibility of trying to elicit ‘tough-guard’ behavior.” Which, again, raises suspicions that the experiment wasn’t as naturalistic as the experimenters implied.]

Brian Resnick

What I want to ask is: What is the case that this experiment should be seen as anything more than an anecdote? I don’t think anyone denies its historical value. It’s an interesting demonstration. Ideas that generated from it are worthwhile to follow up on and to study more carefully. Do you think the experiment itself has a definitive scientific value? If so, what is it?

Philip Zimbardo

It depends what you mean by scientific value. From the beginning, I have always said it’s a demonstration. The only thing that makes it an experiment is the random assignment to prisoners and guards, that’s the independent variable. There is no control group. There’s no comparison group. So it doesn’t fit the standards of what it means to be “an experiment.” It’s a very powerful demonstration of a psychological phenomenon, and it has had relevance.

So, yes, if you want to call it anecdote, that’s one way to demean it. If you want to say, “Is it a scientifically valid conclusion?” I say … it doesn’t have to be scientifically valid. It means it’s a conclusion drawn from this powerful, unique demonstration.

Brian Resnick

Would you agree, as a scientist, that an early demonstration of an idea is bound to be reinterpreted in time, bound to be reevaluated?

Philip Zimbardo

Oh, they should. The essence of science is you don’t believe anything until it has a) been replicated, or b) been critically evaluated, as the study is being done now. I’m hoping a positive consequence of all of this is a better, fuller appreciation of what happened in the Stanford prison study.

Let me just add one thing: There are many, many classic studies that are now all under attack. … by psychologists from a very different domain. It’s curious.

Brian Resnick

I’ve talked to a lot of researchers who are interested in replication, and reevaluating past work. They want to correct the record. I think they’re scared about what happens to the credibility of science if they don’t scrutinize the classics.

And I wonder from your point of view, as a scientist, do you need to be okay with losing control of the narrative of your work as it gets reevaluated?

Philip Zimbardo

Of course. The moment, the moment any of it was published, the moment any of this was put online, which I did as soon as I could, I lost. … You lose control of it. Once it’s out there it’s not in your head anymore. Once it’s out in any public forum, then, of course, I lost control of “the narrative.”

Is it a study with flaws? I was the first to admit that many, many years ago.

Brian Resnick

A study like the prison experiment might just be too big and complicated, with too many inputs, too many variables, to really nail down or understand a single, simple conclusion from it.

Philip Zimbardo

The single conclusion is a broad line: Human behavior, for many people, is much more under the influence of social situational variables than we had ever thought of before.

I will stand by that conclusion for the rest of my life, no matter what anyone says.

Brian Resnick

I’m just unsure if we have the evidence to say if it’s true or not.

There are other researchers who are trying to drill down more into understanding what turns bad behavior on and off. And I’m sure you’re not a fan of him, but Alexander Haslam— [a psychologist who has tried to replicate the prison experiment study, and an academic critic of Zimbardo’s conclusions]

Philip Zimbardo

Oh, God! … no, no, no.

Brian Resnick

You don’t want to talk about him.

Philip Zimbardo

Yeah, okay, No, I don’t want to talk about [him] at all.

Brian Resnick

Well, the gist of what he and his colleagues are arguing is this: Social identity is a really powerful motivator. And it’s perhaps more influential than situational factors. And perhaps the guards in your experiment became cruel because your warden used his authority to foster a social identity within them. [Here’s a new paper with their latest arguments.]

Philip Zimbardo

I reject that. No, no. That’s their shtick, that’s what they’re pushing.

Brian Resnick

You don’t assume good faith on their part?

Philip Zimbardo

I’m not saying good faith. That’s what their claim to fame is the importance of social identity.

Of course people have social identity. But, there’s also something called situational identity. In a particular situation, you begin to play a role. You are the boss, you are the foreman, you are the drill sergeant, you are the fraternity hazing master. And in that role, which is not the usual you, you begin to do something which is role-bound. … This is what anybody in this role does. And your behavior then changes.

Brian Resnick

Is there experimental evidence outside the prison experiment that supports that view?

Philip Zimbardo

The view that situation can make a difference?

Brian Resnick

Yeah. There are plenty of examples in history and current events, but is that something we know as a fact, as an experimental fact?

Philip Zimbardo

I don’t know off the top of my head. …

I’ve always said it’s an interaction. I’m an interactionist. What I’ve said, if you read any of my textbooks, it’s always an interaction between what people bring into a situation, which means genetics and personality, and what the situation brings out in you, which is a social/psychological power of some situations over others. And I will stand by that, my whole career depends on that.

It’s not like I’m mindlessly promoting the situation is dominating everybody.

Brian Resnick

What would you fear might happen if people stop believing in the integrity of the Stanford Prison Experiment?

Philip Zimbardo

The fear is they will lose an important conclusion about the nature of human behavior as being, to some extent, situationally influenced.

Brian Resnick

You’re afraid they’ll lose an important conclusion even though the study is just a demonstration?

Philip Zimbardo

You demonstrate gravity by throwing a ball up and seeing if it comes down. I think you’re insisting on a traditional view of what is scientific, what is a scientific experiment, what is a scientifically validated conclusion. And I am saying from the beginning the Stanford Prison Experiment is a unique and powerful demonstration of how social/situational variables can influence the behavior of some people, some of the time. That’s a very modest conclusion.

Brian Resnick

All of this controversy is happening now because you gave your notes and tapes from the prison experiment to the Stanford archives. That transparency is commendable. Do you regret it?

Philip Zimbardo

No, I don’t regret it. The reason I did it is to make it available for researchers, for anybody, and people have gone through it.

So again, the last thing in the world I need is for people to doubt my honesty, my professional credibility. That’s an attack on me personally, and that I reject and I’m arguing it’s absolutely wrong.

Brian Resnick

Is it okay if we just move on from the Stanford Prison Experiment? Like you said, it’s a demonstration. Maybe we need to ground our understanding of acts of evil in something a little bit more scientific, to be honest.

Philip Zimbardo

At this point, I don’t want anyone to reject that basic conclusion that I’ve said several times in this interview. I don’t want that to be rejected. I would love for there to be better, more scientific evaluation of this conclusion, rather than a bunch of bloggers saying, “We’re gonna shoot it down.”

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