In the wake of the horrific Sandy Hook Elementary School shooting, the country has begun a search for answers. Much of this search has focused on gun laws, a valid point given that the United States has the fewest regulations on guns and the highest gun murder rate of any industrialized country.

But others have focused on the psychology of the shooter – what could possibly cause someone to do something so inhuman? Right now, we really don’t know. We have very little reliable information about Adam Lanza, much less an explanation for the inexplicable.

Some writers have stated definitively in prominent media outlets that one factor is definitively not to blame: violent video games. There is no evidence, they say, that violent video games lead to aggression in real life.

Except there is – plenty of it.

Two meta-analyses, including data on more than 134,000 people, have concluded that violent media causes more aggressive behavior in real life. These are mysteriously absent in the article, which instead mentions a few small studies. This is why scientists do meta-analysis: To find the overall trend across a mass of data, instead of looking at a few studies here and there which may find conflicting results.

These meta-analyses examined both correlational and experimental studies across several cultures, including only methodologically sound studies. The inclusion of experimental studies is important: It means studies have shown that violent video games actually cause aggression. In correlational studies – those that examine violent media consumption and aggression outside the lab – it could be that aggressive kids want to play aggressive games, or that an outside factor such as family background causes both. But an experiment randomly assigns participants to play a violent vs. a non-violent video game, and then measures aggression.

These studies find that playing violent video games does, indeed, cause aggression. The effect is a correlation of about r = .20, considered a small to medium effect in psychology. But even a small to medium effect at the average causes a doubling or tripling of the number of people who are highly aggressive after playing a violent game.

If a large meta-analysis found that kids who eat candy were more likely to hit other kids – with a doubling or tripling in the number who hit really hard -- few people would have a problem saying kids shouldn’t eat candy. Yet because many people enjoy playing video games, they are reluctant to take action to keep people from playing these games – even if it leads to aggression or violence.

It makes sense that the video game industry would not want to believe that their product leads to aggression and violence in real life. But it’s infuritating to see fellow researchers making this claim while cherry-picking which studies they mention. Science is best when it relies not on individual studies but on the preponderance of the evidence. The preponderance of the evidence here is clear, and suggesting otherwise does a disservice to the field and to the public.

Some point out that violent crime has declined over the last twenty years as video games have become more vivid and violent. However, many other powerful factors influence the crime rate, from demographics to changes in policing to drug wars. So this observation tells us very little about the effect of violent video games on behavior.

No, taking away violent video games would not end mass shootings. But the best evidence available suggests that it would reduce real-life aggression. Like all research, these studies are based on averages -- not everyone who plays violent games will become more aggressive. But some will.

Whether the rights of the many should be restricted for the actions of a few is a debatable point. I will leave it to politicians and others to debate exactly what action should be taken; as a psychology researcher, I can only point out the strengths and weaknesses of the evidence. Here, the evidence is very strong. Don’t believe anyone who tells you otherwise.

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