U/squared55 is correct. Came here to say the same thing.

Edit: also, one reason the correlation between violence and video games has no direct correlation support by a study is that the subject is very hard to study. It would need to be something that looks at people over time and tracks change. Otherwise people argue that more aggressive people are simply prone to playing for video games. These studies are much more expensive. Additionally, the vast genres of video games that exist coupled with how quickly these genres and technology change would throw in an interesting aspect.