I understand that you want parents to be informed about their choices for their children, but unfortunately, this kind of study has a history of being (ab)used by groups trying to limit adult's access to this kind of video game, which I have a serious problem with.
First, a few points:
* Many things are "not meant" for teenagers, yet teens acquire (or do) them anyways. Examples include: alcohol, tobacco, watching R-rated movies, etc.
* You may have forgotten just how old kids in highschool are. Specifically, these are teenagers from 14-15 (Grade 9) to 17-18 (Grade 12). While no one under 18 should be playing M-rated games, these individuals are hardly babies.
To answer your bigger question: studies like this are important because teens are a huge video game demographic and are still developing (mentally and physically) during their highschool years. Only now are we seeing such an abundance (and easy access to) video games of all kinds, including violent video games. We must have more such long-term studies in order to understand any potential risks for Jimmy if he spends 3+ hours every day playing a game in which his character "kills" humans (who are mostly foreigners and often in gruesome ways).
You are welcome to mention parental responsibility and voluntary rating guidelines (and these are good points). I'm also against the terrible, blanket attempts at regulating violent video games we've seen in California and other states. However if we discover a link between violent video games and long-term increases in teen aggression then I see nothing wrong with strengthening legislation concerning the sale of M-rated games to minors.
That's the main weakness in the study, btw. It could well be that kids who are prone to violence are more attracted to violent games.
Let's not "throw science under the bus" at all. In fact, there have been studies[1] which show violent crime decreases as access to violent video games increase.
[1]: http://www.telegraph.co.uk/technology/video-games/8798927/Vi...
The study linked above looks at mid/long term effects on a large-ish cohort in a real world setting.
> The study in the article you link to shows that violence decreases in the short term when a violent block buster is released, because violent individuals are busy playing.
That's right, but I fail to see how that's a flaw in the study?
[1]: http://content.usatoday.com/communities/gamehunters/post/201...