A Texas A&M researcher sent GamePolitics a study he recently completed showing little evidence linking violent video games and violent behavior. Christopher Ferguson, a Ph.D faculty member at the university's department of behavioral, applied sciences and criminal justice, conducted a "meta-analysis" of studies associating violent video game exposure with aggressive behaviors. A look at the overall result of studies in the field showed violent video games increase people's aggressive thoughts, not necessarily action.
That's like if you watch a comedy it increases funny thoughts, or after watching a melodrama it increases Japanese RPG thoughts. For the violent game studies to have some validity, the key is for a study to prove that violent video games don't just cause thoughts of violence, but violence itself.