As a psychologist who has studied the effects that media can have on children and adolescents for many years, I am often asked about the role of scientific research in public policy. Good public policy rests on several pillars of support. These include relevant legal precedent, political realities, personal and community values, and in many cases, science. Science can't answer every question, but it can provide useful information for many policy debates. In the case of Schwarzenegger v. EMA, scientific psychology can answer some of the basic questions that policy experts might have, such as whether violent video games have any predictable effects on youth aggression, how large these effects are, and whether there are other predictable factors that can mitigate these effects. Science, however, can only provide information for, but not make decisions about, setting public policy.

At this point in time, there have now been over 100 independent studies of violent video games, including over 130,000 research participants in several countries. As you might expect, not every study shows exactly the same results, but when we look at the studies overall, the preponderance of evidence suggests that people who play violent video games become more desensitized to violence, have more aggressive feelings, more aggressive thoughts, and are more willing to behave aggressively -- especially when provoked. Exposure to aggressive video-game content also reduces cooperative, pro-social behaviors. Although not every study can test whether games cause aggression or whether aggressive people seek out violent games, many studies have tested this question. The best answer at the current time is that both happen. Aggressive people do seek out media violence, and this further reinforces their aggressive tendencies. Similarly, non-aggressive people who consume a lot of media violence change to become more aggressive. This shouldn't be surprising -- it's basic brain science. Whatever you practice, you get better at, including aggression.

So what do scientists mean by "more aggressive"? Critics point out that the studies do not establish a causal link between playing violent games and violent crime. This is actually a very fair criticism -- we do not usually study serious violence or crime (although there are some studies with violent TV). Why not? I can only speak for myself, but I believe that would be an inappropriate level of analysis. It's like saying we should test whether having piano lessons as a child causes people to perform piano at Carnegie Hall. Most children who take piano lessons will never perform at Carnegie Hall. Does that mean that piano lessons had no effect on the children? No. They did indeed get better at playing piano, but they never reached the most extreme level of playing. Similarly, if children practice being alert for hostility, reacting quickly to potential provocations with an aggressive response, and getting rewarded for that in a violent game, they should get better at aggressive attitudes and behaviors -- although not necessarily extreme violence. When bumped in the hallway, they may stop assuming it was an accident and instead assume it had hostile intent, and then their odds of responding aggressively (e.g., insulting the person who bumped them) go up. This is increased aggression, but it's not increased criminal violence. As anyone who has had rumors spread about them or was the victim of bullying can tell you, this is not trivial aggression. It hurts the victims, even though it does not rise to the level of violent behavior or criminal aggression (such as attempted murder).

Therefore, my professional opinion is that science has established that media violence and violent video games are a risk factor for aggression. This does not mean that playing a violent game necessarily causes immediate aggressive behavior. Humans are much more complex than that. Instead, it means that the odds of aggression go up over time, within the broader range of other risk and protective factors, such as poverty, parental involvement, bullying, etc. It is not the largest scientifically identified risk factor for aggression, but neither is it the smallest. Studies have also shown that the effects of playing violent games can be mitigated somewhat by protective factors such as parental monitoring.

It is disturbing to me that people assume that the scientists who conduct research on video games are somehow "biased" and are trying to prove some position or another. I know almost all of the researchers in this area, and this characterization does not fit. They are serious scientists who want to find out what types of effects video games can have (either potentially beneficial or harmful) and what types of things increase the risk of aggression. Most of us researchers play games ourselves and also allow our children to play, so we do not dislike games. For example, my daughters and I play a range of games (mostly nonviolent) on the Wii.