As games become an ever-greater part of our culture, more researchers are conducting studies to try to understand the multitude of effects they can have. Some of the effects games can have are intended, such as providing entertainment. Some of the effects games can have are unintended, such as violent games increasing aggressive thoughts and tendencies. As the research evidence for effects grows, it becomes clearer that parents need to take both the amount of game play and the content of game play seriously.

This year was a banner year for the first longitudinal studies of violent video game effects research. This has been the real missing link in the research literature. Dozens of experimental studies have demonstrated a short-term causal increase in the likelihood of aggression after playing, but we have not known if this became a long-term increase or whether the aggression transferred to the “real” world. Dozens of correlational studies have demonstrated a link between violent game play and “real” world aggression, but it was not known which came first. Longitudinal studies track the same children over time, and can determine which comes first. Several longitudinal studies have now been published.

The first, by Anderson, Gentile, and Buckley, was a study of 430 American third through fifth graders measured twice during the school year. This study found that children who played more violent video games early in the school year became more aggressive (as measured by their peers and teachers) by late in the school year (controlling for prior aggression). Very recently, two studies demonstrated similar results in very different cultures. The journal Pediatrics compared a sample of 181 Japanese 12- to 15-year-olds, 1,050 Japanese 13- to 18-year-olds, and 364 American 9- to 12-year-olds. All were measured at two points in a school year, and all showed similar patterns that playing violent games predicted increases in aggressive behaviors after controlling for prior aggressive behavior.

These longitudinal studies are important, but they have only looked at times of up to six months. This year saw the first published two-year longitudinal studies. Hopf, Huber, and Weiss studied 314 German students (starting in fifth to seventh grades, ending in seventh to ninth grades). This study also measured many other risk factors for aggression, including TV and film