While the effect of violent video games has been an oft-debated subject--some argue that violent games merely draw the attention of those prone to violent behavior--the study found that players were more aggressive than before the research began.

Furthermore, the more they played violent games, the more aggressive the players were in real life. Meanwhile, those that had less exposure to violent games did not see as much of a growth in aggressive behavior.

The study is "pretty good evidence" that violent games lead to violent behavior, commented University of Michigan research director Dr. L. Rowell Huesman.

The research was conduced across three groups: 181 Japanese students ages 12 to 15, 1,050 Japanese students aged 13 to 18, and 364 US kids ages 9 to 12. The Japanese children rated their own aggressive behavior, as did the US group, though additional data on the US group came from peers and teachers.