edit: (repost)
I've looked at the study further and I'm left with some questions. It seems to me that most of the studies with methodological quality (according to the meta-analysis) have been performed by "Craig A. Anderson". He has also exclusively reported findings that support the claim.
The meta-analysis' conclusion is based on the short-term studies, where a person plays the game for 15 minutes and immediate effects are monitored. These are apparently the only studies that show clear effect, unlike longitudinal studies.
My main concern is the lack of insight that is demonstrated. Video gaming is not like its counterparts, you cannot expose a person to 15 minutes of a video game in the same way that you do with film or music. Most of the high-quality studies (of those I looked at) had one person explain how to play the game before they were given access to the content for 15 minutes.
One definition of video games could be; an abstract system wherein the player performs problem solving. Regardless of whether you are shooting rockets at crashing helicopters or more sophisticated environmental puzzles (Portal); you are almost always performing problem solving in some way or another, whether it's abstract or in form of "puzzles". My point is that when you are exposed to such short duration of a video game, you are more occupied with learning that system than fully enjoying the experience. Whether you have been shown how to play is irrelevant, the player must explore and experiment in the system himself/herself in order to become comfortable with it. During this period the player is prone to frustration and irritation, depending on the quality of the game design. There are simply too many influencing variables that I see no mention of.
I'd also like to know how they researched Japanese gaming, whether proper industry professionals were consulted. The method by which they define violent games and non-violent games are cringe-worthy, the definition also differs greatly in the these studies. Some would define Super Mario Bros. as a violent video game while others set the bar to decapitation and gore. Some statements are outright incorrect. It might be that some video games are risk factor for violent behavior, but this meta-analysis has done little to convince me so far.
Besides, meta-studies doesn't have a history for being well done or good research. Even organizations like WHO are capable of
messing these up. (This is a medical study, so that's even worse).