In August 1971, Philip Zimbardo began an experiment that became famous in psychology textbooks for its discoveries, as well as the damaging evidence that later brought the study's legitimacy into question. The Stanford prison experiment consisted of around 20 student volunteers acting as guards and prisoners in a “prison” located in the basement of Stanford University’s psychology department. Although Zimbardo scheduled the experiment to last for two weeks, he was forced to end it after only six days due to unethical testing conditions.
Zimbardo, as well as many psychologists and criminologists, believed the experiment was a success. Many claimed it proved a person’s situation affects their behavior as much as their personality, sometimes with even greater influence. It was interpreted as evidence that individuals aren’t responsible for their actions, but rather that the environment, people, and activity around them cause negative behaviors. Ever since Zimbardo published his celebrated study, however, others have claimed the famous psychology experiment may have suffered several biases that would deem it scientifically inaccurate.
Zimbardo Shaped The Experiment To Fit His Desired Results
Through the Stanford prison experiment, Zimbardo wanted to prove that people put into a situation in which they hold power over others will unknowingly alter their behavior. Unfortunately, in order to do so, Zimbardo influenced his subjects toward that outcome. In addition to making the participants aware they were part of an experiment and required to play certain roles, he created extreme differences between the participants acting as guards and those acting as prisoners.
Allegedly due to Zimbardo's coaching, guards humiliated prisoners, forced them to relieve themselves in buckets, fed them only small amounts of food, and made them wear bags over their heads when outside their cells. They also chained inmates, made them wear stockings on their heads instead of shaving their hair, and didn't allow them to wear underwear under their smocks.
While the inmates underwent near-constant humiliation, Zimbardo dressed the guards in matching uniforms, giving them a sense of authority and solidarity as a team. It's possible the difference between the two groups' treatment helped shape their behavior by heightening or lowering their sense of power in the situation.
The Experiment's Published Results Were Largely Based On Anecdotal EvidencePhoto: The Stanford Prison Experiment / IFC Films
According to Zimbardo, the Stanford prison experiment functioned as a demonstration, not a carefully controlled scientific test. "The only thing that makes it an experiment is the random assignment to prisoners and guards, that’s the independent variable," he said. "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.'"
Rather than presenting a hypothesis and then testing it with a reproducible experiment, Zimbardo's study consisted of anecdotes about what occurred during the experiment. Despite the fact that it didn't reach a scientifically proven conclusion, Zimbardo insisted the experiment proved some valid points: "...It doesn’t have to be scientifically valid. It means it’s a conclusion drawn from this powerful, unique demonstration."
Guards Knew Their Actions Would 'Help' The Study
At a meeting prior to the start of the experiment, Zimbardo made sure the students acting as guards knew they were there to make the experience realistic. Zimbardo told them, "We can create boredom. We can create a sense of frustration. We can create fear in them, to some degree... We have total power in the situation. They have none."
Although Zimbardo claimed the guards' behavior was their own idea, documents later suggest they had some inspiration. Undergraduate student and acting warden David Jaffe gave the guards a list of rules to enforce, such as not referring to the situation as an experiment and calling inmates by number rather than their name. According to Professor David Aodio, guards were also aware of the outcome Zimbardo wanted to achieve, which may have influenced their behavior.
Zimbardo insisted no one coached the guards since their behavior varied. "One or two guards on each shift became progressively meaner over time, others maintained a more even-tempered style, and a few were considered 'good guards' from the prisoners' perspectives," he wrote. "The fact that some guards remained 'good guards' throughout the study shows that cruel guards chose to act on their own initiative."
The Study's Sample Size Was Small And Very Narrow
For his experiment, Zimbardo recruited 24 students out of around 75 volunteers. Except for one Asian man, all of these students were male, middle-class, and white. Despite this small sampling of people, Zimbardo used their behavior to presume all of society would act in a similar way.
In order to pick out the behavioral differences between subjects and attain more accurate results, scientists routinely conduct their experiments using large numbers of people. Many scientists conducting a similar experiment might have used more participants or run the experiment several times to examine a larger sample of people; however, since Zimbardo's sample gave him the results he wanted, he failed to take the experiment any further.