By Craig Anderson and Brad Bushman

As well-known scholars of media violence and its impact on real-world behavior, we are flooded with calls from journalists whenever an incident of mass violence occurs, such as the tragedies at Columbine or Sandy Hook. We try to oblige callers as best we can. Yet to judge from the tenor of many of these conversations, our position on media violence continues to be seen as much more “controversial” than it actually is.

To clarify the issues, we and a number of our colleagues recently conducted a comprehensive review of the six-decade long research literature on the topic. Our conclusion: Media violence is an important causal factor for increased aggression in both the short- and long-term, and is significantly related to violent criminal behavior. (For a summary of that research, see here.)

But there’s an important caveat: While the evidence of a causal link is strong, the size of the effect is modest. Think of second-hand smoking: The evidence unambiguously shows that you have a much greater lifetime risk of developing lung cancer if you are regularly exposed to smoking than if you aren’t. But compared to actual smokers, relatively few second-hand smokers develop lung cancer. The evidence is clear, but the size of the effect is modest.

So how strong is the link between media and real-world violence? Effects on behavior are always more difficult to tease out than medical outcomes. A heavy diet of violent movies, television, and video games is just one of several risk factors inducing violence, but it is not a trivial one. It is not as big a risk factor as joining a violent gang, but it is as large as many other risk factors for violence, such as having abusive parents.

No psychologist can say with certainty what goes on in the minds of mass killers. Incidents like Sandy Hook are sufficiently rare that it is impossible to generalize with certainty about the various risk factors involved or the motivations of the people who commit them. But a variety of studies dating back six decades shows that media violence is bad for the developing brain, and contributes to our nation’s elevated levels of assault, gang fighting, sexual violence, robbery and murder:

• Experimental studies have shown that even brief exposure to media violence can increase aggressive thinking and behavior. For example, playing a children's violent video game for 20 minutes increased the aggression levels of 9-12 year old children by over 47 percent, compared to children who played a nonviolent children's game.

• Brief exposure can also reduce our ability to empathize with and to help people who are victims of violence. For example, college students who had just played a violent video game took over three times longer to come to the aid of a person who had been injured in a fight compared to students who had just played a nonviolent game. After watching a violent movie, adult moviegoers were slower to help an injured stranger who dropped her crutches, whereas those who watched a nonviolent film were equally helpful before and after the movie.

• Longitudinal studies follow large numbers of people over an extended period of time, while repeatedly measuring media habits and levels of aggression. They consistently show that children with similar levels of “innate” aggression become more violent the more they are exposed to violent media.

• Intervention studies among children and teens show that reducing exposure to violent media for periods as little as five weeks decreases lab-based and observed aggression, even among high-risk youth.

The amount of media that children consume continues to drift upward. Children age eight to 18 now spend an average of 7 hours and 38 minutes with media each day, compared to 6 hours and 19 minutes in 1999. An average American child will see 200,000 violent acts and 16,000 murders on TV by age 18.

Most Americans understand that something is wrong with this picture. In a recent poll, 84 percent agreed that depictions of violence contribute either “some” or “a lot” to violence in society. We believe that a few common-sense proposals could significantly reduce public violence and contribute to a saner, less dangerous world.

First, we need to develop a more consistent and thoughtful media rating system. With each media type featuring its own system, we’ve developed an alphabet soup of ratings that leaves everyone confused. (It doesn’t help, surely, that the systems are devised and assigned by the media companies themselves.) The President and Congress need to appoint a commission of public health officials, psychologists, criminologists and industry leaders to develop a consistent, scientifically based media rating system. We should then actively promote the importance of the ratings—including statements about the real effects of media violence— through a public education and outreach campaign.

We should expand media literacy programs in schools, helping children and adolescents to understand why violence is undesirable, impractical and rarely works well in the real world. We should do more outreach to parents: How many know that pediatricians recommend that infants under two years of age should have no screen time, and recommend no more than an hour or two for older children?

Past proposals to improve public health outcomes have proven remarkably successful. In our lifetime, the U.S. has more than halved the rate of smoking and drunken driving, discouraged second-hand smoking, and increased seatbelt use. There is no reason we can’t do the same for media violence. Our children will thank us for it.

 Craig Anderson is Distinguished Professor & Director, Center for the Study of Violence, at Iowa State University. Brad Bushman is Professor of Communication and Psychology, Margaret Hall and Robert Randal Rinehart Chair of Mass Communication, at The Ohio State University.

Bushman et als recent survey of media researchers, parents and pediatricians found that solid majorities agree that exposure to violent media can increase aggression in children.