Snipers. Rape. Cars targeting pedestrians. Heads exploding in a shower of gore.

These scenes can all be found in violent video games, and this month the Journal of Adolescence published several studies looking at their effects on youth. I was involved in one study (Gentile, Lynch, Linder, & Walsh, 2004). After looking at more than 600 Grade 8 and Grade 9 students, we found that playing a lot of violent video games was a serious risk factor linked with children's anti-social and aggressive behaviour -- even after controlling for the amount the children play, their gender and whether they have naturally hostile personalities. Surprisingly, even the kids who are not naturally aggressive are almost 10 times more likely, if they play a lot of violent video games, to get into physical fights than kids who do not.

Our study is only one of about 40 peer-reviewed, published studies that demonstrate that playing violent video games increases aggressive feelings and behaviours. These games are not the Pac-Man and Pong of earlier generations; as technology has advanced, violent video games have become extremely graphic (in Grand Theft Auto: Vice City, a man encounters a prostitute, has sex and then beats her to death to get his money back).

Although such ultraviolent video games carry an M (mature) rating, a recent study by the American Federal Trade Commission found that children can buy them easily. In a separate study of nearly 800 Grade 4 to Grade 8 kids, 87 per cent of boys reported that they play M-rated games, and one in five admitted that he had bought an M-rated game without parental knowledge.

As the research evidence about the negative effects of violent games become more compelling, parents, educators, and policy-makers are increasingly concerned about what to do. From my perspective, there are three pillars of responsibility: the video-game industry, the rental and retail industry and parents.

The video-game industry must clearly and accurately label the content of games, so that parents know what they are getting before buying. Recently, the authors of a study of teen-rated games pointed out that there is a "significant amount of content in T-rated video games that might surprise adolescent players and their parents" (including violent sexual themes and drug use).The second responsibility of the video-game industry is to market its products appropriately. Yet advertisements for M-rated games have appeared in Sports Illustrated for Kids. It's unfair of the industry to label games as "not for kids" while marketing them to children. True, the industry has taken steps to reduce this, but there is still significant room for improvement.

The rental and retail industries also have responsibilities. First, they must create policies under which children under 17 may not buy or rent M-rated games without parental permission. Many stores, including large chains and superstores, have no such policies. Some of those who do don't enforce them. In one sting operation conducted by the National Institute on Media and the Family, children as young as seven encountered no problems in about half of their attempts to buy M-rated games. Parents should be able to expect that stores won't allow children access to M-rated games -- just as they expect movie theatres won't give children access to an R-rated movie when parents drop them off at the theatre.

The third pillar of responsibility is parents -- who must start by educating themselves about the differences among video-game ratings ("E" for everyone, "T" for teen, "M" for mature) and to learn why it is important to pay attention to the ratings. Here is where the research is so useful: Studies show that both amount and content matter. Children who play a lot of video games get poorer grades in school. Children who play violent games appear to become more aggressive over time.

Finally, parents need to act on their knowledge. Just as playing violent games is what scientists call a risk factor for negative outcomes for children, active parental involvement in children's video-game habits acts as a protective factor.

Should local, state, province or federal governments get involved?

The video-game industry is responsive to some parental concerns and to pressure from politicians. Still, there probably are areas where legislation could be helpful without rising to the level of censorship. Just like the 1996 U.S. Telecommunications Act, which mandated that TV shows be rated, new legislation could require that the TV, movie, and video-game industries create a universal rating system so that parents need not learn the full alphabet soup of different systems.

Legislation could also mandate that the ratings be administered independently of each medium (currently, U.S. TV ratings are assigned by the TV networks, movie ratings by the Motion Picture Association of America, etc.) Legislation might also mandate the creation of an independent ratings-review board to do research on the validity of the ratings and maintain standards.

There have been legislative attempts to restrict the sale of M-rated games to minors in the United States. This approach seems reasonable: The video-game industry itself acknowledges that these games are not for children (hence the M-rating), and legal precedent in the United States has established that the government has an entirely appropriate role in limiting the influences and activities to which children are exposed.

In my country, state and local authorities routinely restrict minors' access to tobacco, guns, pornography, and gambling. In fact, the U.S. Supreme Court, in Ginsberg v. New York (1968), upheld limiting minors' access to pornography on the basis of whether it was "rational for the legislature to find that the minors' exposure to [such] material might be harmful [emphasis added]."

The research conducted to date has clearly met that test, and shows that, for some children, exposure to violent media is harmful. Oddly, the video-game industry has fought every legislative attempt to restrict the sale of M-rated games to minors. That is puzzling; it suggests that the industry is unwilling to stand behind its own ratings. That fact alone makes it clear that parents should be very cautious before they buy that next "hot" game for their child.

Douglas A. Gentile is director of research at the National Institute on Media and the Family, and an assistant professor of psychology at Iowa State University.