http://www.sciencemag.org/news/2021/02/research-linking-violent-entertainment-aggression-retracted-after-scrutiny

Do violent movies like Sin City lead to aggression? Retracted studies have muddied the debate.

As Samuel West combed through a paper that found a link between watching cartoon violence and aggression in children, he noticed something odd about the study participants. There were more than 3000—an unusually large number—and they were all 10 years old. “It was just too perfect,” says West, a Ph.D. student in social psychology at Virginia Commonwealth University.