When things start to get crazy, the “bystander effect” can kick in. As seen in many public incidents (notably when bystanders took photos of a man about to be killed on NYC train tracks), the bystander effect is generally considered a powerful force in determining whether someone intervenes in a dramatic indecent. Basically, people are less likely to intervene if others are around—they assume someone else will deal with the problem. That said, a recent study by graduate student Michael Parks of Penn State shows that the bystander effect may not be as strong as was once thought.  In an interview for MedicalXpress, Parks explains what he saw in observing bar fights:

These bystanders used nonaggressive interventions to break up about 65 percent of the fights between two aggressive males. Most bystander interventions were classified as nonviolent interventions, which included verbally stopping the fight, or separating the fighters.

Parks worked with Wayne Osgood and Richard Felson, both professors of Penn State; Samantha Wells of the University of Ontario; and Kathryn Graham of the University of Toronto. The team’s study found that bystanders were most likely to intervene when they felt the violence was getting “too severe.” Bystanders were most likely to step in when it was male-to-male aggression, since most assume the violence escalates most quickly. Surprisingly, bystanders generally avoided breaking up male-to-female aggression (though, anecdotally, police officers do say intervening in partner violence is risky, since both partners may turn their aggression on the interloper).

“It seems a little upsetting that people didn’t intervene in incidents that involved a man harassing a woman, but the results showed that this was indeed the case,” said Parks. “Our data showed that this type of violence had the lowest level of severity, so one explanation for the lack of intervention in these incidents is that third parties perceived that the events won’t escalate into higher levels of violence, something that does not have the potential to be dangerous or an emergency.”