The young men who opened fire at Columbine High School, at the movie theater in Aurora, Colo., and in other massacres had this in common: they were video gamers who seemed to be acting out some dark digital fantasy. It was as if all that exposure to computerized violence gave them the idea to go on a rampage — or at least fueled their urges.

But did it really?

Social scientists have been studying and debating the effects of media violence on behavior since the 1950s, and video games in particular since the 1980s. The issue is especially relevant today, because the games are more realistic and bloodier than ever, and because most American boys play them at some point. Girls play at lower rates and are significantly less likely to play violent games.

A burst of new research has begun to clarify what can and cannot be said about the effects of violent gaming. Playing the games can and does stir hostile urges and mildly aggressive behavior in the short term. Moreover, youngsters who develop a gaming habit can become slightly more aggressive — as measured by clashes with peers, for instance — at least over a period of a year or two.

Yet it is not at all clear whether, over longer periods, such a habit increases the likelihood that a person will commit a violent crime, like murder, rape, or assault, much less a Newtown-like massacre. (Such calculated rampages are too rare to study in any rigorous way, researchers agree.)