Video games are a major part of most teens’ lives. As many as 90 percent of U.S. teens play them. Boys are more likely to play than girls. And more violent games, such as Call of Duty or Grand Theft Auto, are among the most popular. All this has led adults to worry that violent games are making teens act violently in real life. In fact, a careful new study finds, this is not the case.

Many scientific studies have scouted for links between video-game violence and real-world violence. It might seem logical that playing violent games would have lasting effects on the brain. And those effects might influence how someone acts. But research has shown mixed results. Some studies found a strong effect. Others found none. Those conflicting findings have confused many people — teens, parents and scientists included.

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Psychologists Andrew Przybylski and Netta Weinstein felt that a more carefully designed study might clear the picture. Przybylski works at the University of Oxford in England, and Weinstein is at Cardiff University in Wales.

The two recruited 1,004 teens in the United Kingdom. All were 14 or 15 years old. The teens’ parents or guardians also took part. These adults answered questions about their teen’s aggressive behavior.

The teens answered a different set of questions. Some asked about their feelings. For example, would they hit someone if they got angry enough? Did they argue a lot? Did they tend to lose their temper? These responses in fact closely matched what their parents or guardians had said. The researchers now felt confident they had an accurate measure of each teen’s aggression.

The students also answered questions about the video games they played. What kinds did they play? How much time did they play them? In all, these kids reported playing 1,596 different games. Based on the games’ ratings, almost two-thirds of them were deemed violent.

Researchers then compared levels of video-game violence with a teen’s aggression. They looked for two potential links. One was a direct relationship — that teens who spent more time playing violent video games were more aggressive. The other was a “tipping point” — signs that teens were more aggressive — but only after spending a certain threshold amount of time playing violent games.

In the end, the researchers found no evidence for either.

“Evidence that people point to as showing games make young people aggressive is very low quality,” Przybylski says. “Because our study was done rigorously,” he believes that “it provided a fair test of the idea that games might cause aggression.”

He and Weinstein shared their findings online February 13 in Royal Society Open Science.

The potential role for bias

Przybylski and Weinstein had worried that earlier studies of video games might have been biased. That is, the researchers might have gone into a study expecting one particular result. If they did, they might try analyzing their data in different ways until they got that result. After all, looking at data in many different ways ups the chance researchers will find something; it just might not be a valid finding.

Such multiple analyses had been especially common in studies that found a strong link between video-game violence and teen aggression, Przybylski and Weinstein note. Perhaps these researchers had used analyses that gave them the results they had expected. Hoping to avoid such biases, Przybylski and Weinstein registered their experiment and analyses before they started.

This pre-registration is a process that lets other scientists review a study before it takes place.

Peer review is an important part of science. But often it happens only at the end, once a study is over. A pre-registered study gets peer-reviewed twice. Experts review the study ahead of time. This ensures that scientists will analyze their data in the best way for their experiment. Later, the researchers can’t change their minds about what analyses they’ll use. That helps protect their study from bias. Later, peer reviewers will analyze the study and its findings.

Putting it to the test

“A lot of the attention from this study has been about the findings,” says Randy McCarthy. He’s a psychologist at Northern Illinois University in DeKalb. “However,” he says, “I strongly believe the major strengths of the article are the methods.” Specifically, he’s impressed by the pre-registration and early stage of peer review. “The methods are what give us confidence in the findings,” he says.

Still, the study only looked at a single point in time for the teen gamers. That’s a drawback, he notes, because the researchers still can’t say whether violent games make teens more aggressive over time. Future studies that follow gamers over months or years could help answer this question, he says.

Teens may feel angry after playing video games, Przybylski says. But he thinks that’s due to competition. People “are more likely to get angry after losing,” he points out.

“Games are meant to be fun,” he says. “If they stress you out, or you don’t feel good about them, spend your time doing something else.”