How were the participants selected for Zimbardo's Prison study?

In Zimbardo's Prison study, participants were initially screened to ensure they were psychologically healthy and physically fit. After this screening process, the participants were randomly assigned to either the role of prisoner or guard. This method of random assignment is crucial in experimental research because it helps eliminate bias and ensures that the groups are comparable at the start of the study. Assigning roles randomly meant that any differences observed between the behaviors of the "guards" and "prisoners" could be attributed to the situational pressures of their assigned roles rather than any pre-existing characteristics of the individuals themselves. This design allowed researchers to investigate the psychological effects of perceived power in a simulated prison environment effectively.