Before you read, this is an article from  videogamevoters.org. The link is at the bottom. It is a pretty long read.

"WHAT ABOUT YOUTH VIOLENCE? LOOKING AT THE STATISTICS

• Violent crime, particularly among the young, has decreased dramatically since the early 1990s while video games have steadily increased in popularity and use.
• Dr. Joanne Savage reviewed the research purporting to show negative effects of media violence on youth. She concluded that there is no causal link between media violence and violent crime. From her 2004 article, "Does Viewing Violent Media Really Cause Criminal Violence? A Methodological Review" that appeared in the journal Aggression and Violent Behavior:
  The question addressed here is not whether or not the effect is plausible, but whether the effect has been demonstrated convincingly in the scientific literature and the answer is 'not so far.'...At this point it must be said, however, that there is little evidence in favor of focusing on media violence as a means of remedying our violent crime problem. Certainly video games haven't had any significant impact on real-world crime.
  
• Many games with violent content and sold in the United States and some with far more violence � are also sold in foreign markets. However, the incidence of violent crime in these non-U.S. markets is considerably lower than in the United States. This suggests that the cause of violent crime lies elsewhere.

WHAT DOES THE SCIENCE SAY? INDEPENDENT RESEARCH FINDINGS

Williams, D. & Skoric, M. "Internet Fantasy Violence: A Test of Aggression in an Online Games." 2005.

Williams and Skoric set out to determine the effects, if any, of engaging in a violent massive multiplayer online role-playing game. They found that there was no effect on levels of aggressiveness or in belief and behaviors of the gamers.

They wrote, "Research on violent video games suggests that play leads to aggressive behavior. A longitudinal study of an online violent video game with a control group tested for changes in aggressive cognitions and behaviors. The findings did not support the assertion that a violent game will cause substantial increases in real-world aggression." The results determined that, "...game play controlling for gender, age, and time one aggression scores - was not a significant predictor of aggressive cognitions. Compared to the control group, participants after the experiment were not statistically different in their normative beliefs on aggression than they were before playing the game."

Olson, C. "Media Violence Research and Youth Violence Data: Why Do They Conflict?" Academic Psychiatry, 28:2. 2004.

Cheryl K. Olson, professor of Psychiatry at the Harvard Medical School's Center for Mental Health and Media, examines statements about the relation between violent video games and real-life violence in a 2004 article in the journal Academic Psychiatry.

First, Dr. Olson notes that "...there is no evidence that targeted violence has increased in America's schools. While such attacks have occurred in the past, they were and are extremely rare events." She goes on to write that, "There's no indication that violence rose in lockstep with the spread of violent games."

Dr. Olson then details the limitations of current studies on games and youth violence, including: vague definitions of aggression; failure to put use of violent media in context with other known contributors to aggression (such as illegal substance use and family poverty); results which are difficult to generalize to the real world; small, non-random, non-representative samples; and lack of consideration of moderating factors such as the subjects' age or developmental stage.

Dr. Olson concludes: "In summary, it's very difficult to document whether and how violent video and computer games contribute to serious violence such as criminal assault and murder." She writes, "It's time to move beyond blanket condemnations and frightening anecdotes and focus on developing targeted educational and policy interventions based on solid data. As with the entertainment of earlier generations, we may look back on some of today's games with nostalgia, and our grandchildren may wonder what the fuss was about."

Bensley, L. & Van Eeenwyk, J. "Video Games and Real-Life Aggression: Review of the Literature." Olympia, WA: Washington State Department of Health. 2002.

In a 2002 presentation that updated their earlier comprehensive review of the literature on games and violence, Dr. Van Eeenwyk from the Washington State Department of Health presented information indicating that "after controlling for psychosocial factors, association between aggression and playing video games was not statistically significant." This review was based on available objective research and was conducted by the State of Washington at the request of the state legislature.

Egenfeldt-Nielsen, S., et al. "Playing With Fire: How Do Computer Games Influence the Player?" Commissioned by the Danish Government and published by the Unesco Clearinghouse on Children, Youth and Media. 2004.

In their review of the existing body of research commissioned by the Danish Ministry of Culture, the authors determined that the results of research into the effects of violent games have "often pointed in different directions." The authors state: "...the studies that purport to show [a connection from violent games to violent behavior] have been exposed to serious and continuing criticism.

This criticism is primarily that it is an oversimplification to perceive computer games as a phenomenon that can be isolated from the player's everyday life." Further, the authors conclude that: "It is not possible to say anything conclusive about the potentially adverse effects of violent games. The empirical evidence is too limited and the criticism of the extant research too serious.We can say that the question of the extent to which computer games in general have an adverse effect on all or on many gamers is too broad for a specific answer."

Baldaro, B., et al. "Aggressive and Non-Violent Videogames: Short-Term Psychological and Cardiovascular Effects on Habitual Players." Stress and Health, Vol. 20, pp. 203-208. 2004.

Researchers set out to evaluate the short-term effects of playing violent and non-violent videogames among young adults. The results of the study determined that there were no increases in the participants' hostility measurements. Specifically, the authors write: "The increasingly widespread use of videogames among young people has led to many studies into their potential negative effects.

Research into progress in school and personality of young videogame players has partly eased some general worries. Owning videogames does not in fact seem to have negative effects on aggressive human behaviour. The results of [this] study showed a range of short-term effects of playing violent and non-violent video games on arterial pressure and on the state anxiety of subject, but not on hostility measurements (emphasis added)."

Vastag, B. "Does Video Game Violence Sow Aggression?" Journal of the American Medical Association. 2004.

In a summary of research, researcher, Brian Vastag, details the results of major studies and their findings. His conclusion is that:

• Consensus is lacking on whether video games with violent content fuel aggressive behavior in children and adolescents...
• If video games do increase violent tendencies outside the laboratory, the explosion of gaming over the past decade from $3.2 billion in sales in 1995 to $7 billion in 2003, according to industry figures would suggest a parallel trend in youth violence. Instead, youth violence has been decreasing.

Tremblay, R. "Physical Aggression During Early Childhood: Trajectories and Predictors." Pediatrics. 2004.

Dr. Richard Tremblay, professor of Pediatrics, Psychiatry and Psychology, Canada Research Chair in Child Development, and Director of the Centre of Excellence for Early Childhood Development and widely considered one of the world's leaders in aggression studies, has conducted research on thousands of subjects to determine that:

• Most children have initiated the use of physical aggression during infancy, and most will learn to use alternatives in the following years before they enter primary school. Humans seem to learn to regulate the use of physical aggression during the preschool years. Those who do not appear to be at highest risk of serious violent behavior during adolescence and adulthood.
• Results from the present study indicate that children at highest risk of not learning to regulate physical aggression in early childhood have mothers with a history of antisocial behavior during their school years, mothers who start childbearing early and who smoke during pregnancy; parents who have low income, and have serious problems living together.

Sternheimer, K. "It's Not the Media: The Truth About Pop Culture's Influence on Children." 2003.

In her book, Dr. Sternheimer researches why the media is a constant target of attack and focal point of blame for society's ills. She looks deeper into our societal dilemmas to see what other common factors could be affecting children. Blaming media for changes in childhood and social problems has shifted our public conversation away from addressing the real problems that impact children's lives. The most pressing crisis facing American children is not media culture but poverty [p. 4]....We want research to support our fear so badly that even a minor study filled with flaws will be published and circulated throughout the news media [p. 112]

Dr. Sternheimer concluded that "violent video games are a lot like dreams where we work out our fears or anxieties without actually ever engaging in them." [p.114]

Office of the Surgeon General. "Youth Violence: A Report of the Surgeon General." U.S. Department of Health and Human Services. 2001.

After examining the science on violence in video games, the Surgeon General concluded:
The overall effect size for both randomized and correlational studies was small for physical aggression and moderate for aggressive thinking... The impact of video games on violent behavior remains to be determined. (p.92) "