Mind & EverydayFact
The most famous prison study is now considered methodologically hollow.
Zimbardo's 1971 study was stopped after six days. In 2019 Thibault Le Texier used the archives to show guards were explicitly told to act tough and the conclusions were largely written in advance. A 2002 BBC restaging without such instructions produced entirely different results.
Useful: A result is only as good as what the experimenters told participants beforehand.
Source: en.wikipedia.org