Most introductory psychology textbooks discuss Philip Zimbardo’s Stanford Prison Experiment, but many do not mention criticisms of the famous experiment and those that do provide only minimal critical discussions, according to a new study.

“Introductory textbooks cover hundreds of topics and cite thousands of references so their authors may not be conversant with all relevant studies on the hundreds of topics, especially given that introductory psychology texts are revised on a short cycle, typically 3 years. If this is the case and introductory text authors are not aware of the entirety of the criticism of the SPE, then this article should help to rectify that situation,” Richard A. Griggs wrote in his study, which was published in the journal Teaching of Psychology.

In 1971, Zimbardo and his students attempted to examine the psychological effects of prison life by creating their own mock prison in the basement of Jordan Hall, with 24 college students acting as the guards and prisoners.

“We based our experiment on an in-depth analysis of the prison situation, developed after hundreds of hours of discussion with Carlo Prescott (our ex-con consultant), parole officers and correctional personnel, and after reviewing much of the existing literature on prisons and concentration camps,” Zimbardo explained.

But the guards — dressed in uniforms from a military surplus store and armed with wooden batons — started to adopt abusive practices just days after the experiment began. Things got so out of hand that the two-week experiment was prematurely ended after only six days.

Zimbardo concluded that situational forces could transform normal, decent people into perpetrators of evil. Otherwise ordinary students placed in an environment in which they were given absolute control with no rules other than to maintain order became authoritarian sadists not because they were “bad apples” but because their social role as guards called for such behavior.

However, the study and its “situationist interpretation” have garnered significant amounts of criticism.

Firstly, Zimbardo, who acted as the prison’s superintendent, appears to have instructed the guards, both explicitly and implicitly, how to carry out their duties. Zimbardo “gave the guards an orientation that seems to have provided clear guidance about how they should behave,” Griggs noted.

In addition, only one-third of the guards in the Stanford Prison Experiment abused the prisoners. Psychologist Erich Fromm argued that this finding flies in the face of the Zimbardo’s situationist interpretation.

“If in spite of the whole spirit of this mock prison which, according to the concept of the experiment was meant to be degrading and humiliating (obviously the guards must have caught on to this immediately), two thirds of the guards did not commit sadistic acts for personal ‘kicks,’ the experiment seems rather to prove that one can not transform people so easily into sadists by providing them with the proper situation,” he remarked.

In his study, Griggs listed slew of other criticisms: “The SPE has also been criticized for the lack of generalizability and ecological validity (e.g., Fromm, 1973), the possibility of participant selection bias (Carnahan & McFarland, 2007; McFarland & Carnahan, 2009), for breaching research ethics (e.g.,Savin, 1973), for providing no satisfactory account of the individual differences observed (McGreal, 2013), and for being a pseudoscientific experiment that is more aptly described as Kafkaesque absurdist performance.”

Griggs’ review of 13 introductory psychology textbooks found that 11 of them discussed the Stanford Prison Experiment. Despite all these criticisms, 5 textbooks did not contain any criticism of the experiment, and the other 6 provided “very minimal” discussions of the study’s flaws.

Authors might omit criticisms of the famous experiment due to space constraints, Griggs said, or because they are unaware of the criticisms or convinced by Zimbardo’s rebuttals.

“Given the abundance of criticism available, why might introductory text authors provide such limited coverage of it?” Griggs wrote. “One possibility would be lack of knowledge of the criticism. This lack of knowledge, however, would not seem very likely, given the sheer amount of criticism that has been published and the prominence of the journals in which it has appeared. Nevertheless, it may be the case that the text authors are not aware of the extent of the criticism, and if they were, they would likely revise their coverage of the SPE or possibly even omit it.”

Watch Zimbardo explain his views on human behaviors and evil below: