A review of research in the 1990s concludes that there is a positive and significant correlation between television violence and aggressive behavior, regardless of age. Media exposure in general also increases alcohol and tobacco use, and leads to earlier onset of sexual activity.  Viewing media violence is thought to increase hostile feelings, decrease emotional response to the depiction of violence and injury and lead to violent behavior through imitation.  A 15-year study found that childhood exposure to media violence, identification with aggressive TV characters and perceiving TV violence as real all predict aggressive behavior in young adults.  A U.S. surgeon general’s report on youth violence said that while there is strong evidence that exposure to media violence can increase children’s aggressive behavior in the short term, many questions remain regarding long-term effects on violent behavior.  The effect that media violence has on behavior is greater that the effect of lead exposure to low IQ in children, is twice the size of the relationship between calcium intake and bone density, and was second only to the association between smoking and lung cancer, according to one frequently cited study.  Some evidence suggests that children who are more aggressive are drawn to watching more violence. But evidence is stronger that watching media violence is a precursor to increased aggression, said the U.S. surgeon general. 
A large body of experimental, correlational and long-term research on TV and movie violence indicates that media violence causes real-world aggression.  Adolescents and young adults who watch a lot of television are more likely to commit aggressive acts against others, according to an article in Science.  Playing violent video games causes increases in aggressive behavior as well as in several other aggression-related variables and causes decreases in socially acceptable behavior.  Regardless of attempts by government and other interested groups to limit the amount of violence reaching American families, parents play a critical role in guiding what reaches their children.  Most evidence indicates that violent behavior seldom results from a single cause, but rather from multiple factors converging over time, the surgeon general’s report says. The influence of the mass media is best viewed as one of the many potential factors that help to shape behavior, including violent behavior. 
Seeing Is Believing… Violent content on TV, the Internet, movies or video games tells children that people are vindictive, negative events are deliberate acts of malice, and retaliation is a valid response to conflict, says Craig Anderson, a leading researcher on the effects of media violence on children. “People learn and content matters,” says Anderson, a professor of psychology at Iowa State University. According to the American Academy of Pediatrics, “More than 1,000 scientific studies and reviews conclude that significant exposure to media violence increases the risk of aggressive behavior in certain children,... desensitizes them to violence and makes them believe that the world is a ‘meaner and scarier’ place than it is.”  One study followed children from elementary school to their early 20s, reporting that “childhood exposure to media violence predicts young adult aggressive behavior in both males and females.”  However, some argue that the real effect is minimal. One untested hypothesis is that exposure to media violence actually provides a healthy release for the frightening emotions of adolescence. Anderson maintains that such a view is simply wrong. A 2001 U.S. surgeon general’s report on youth violence found only modest associations between exposure and aggression, but it focused on overt, criminal violence committed by young people rather than broader measures of aggression. How can the effects of media violence be minimized? Many agree that censorship is both undesirable and unlikely. “Parental influence is far more powerful than anything in the media,” says educational technology consultant Jennifer Borse. “If the parents are raising their children well, they can make kids more aware of what they are seeing and the effect it has on them.”
Both parents and children might become more media literate — more aware of what they are seeing and more conscious of the effect it has on them, Borse says. Parents can view things with their kids and help interpret content, explaining that what they are seeing is not real and that in real life, people find other, non-violent ways to settle conflict. In fact, studies have shown that parents frequently have no clue about what their children actually watch. So parents need to know and guide the ingredients in children’s media diets, just as they supervise the contents of a healthy food selection at home, says Anderson. Finally, researchers suggest that parents direct their children away from the couch and electronic media, and more toward activities with other people.