As it turns out, there was a Harvard study on this topic (it was federally funded!). And the authors of that study have now published a book on their findings. (published April 15, 2008)
Even if your kid does play the game ... well, it might not warp him or her for life. The study was conducted by a husband-and-wife team who are co-founders of the Center for Mental Health and Media and serve on the psychiatry faculty of Harvard Medical School. The findings are published in their new book, titled "Grand Theft Childhood."...Olson said, real-world statistics paint the picture as vividly as any research. "In some ways, it's common sense," she said. "Game playing has been going up and violence has been going down."
The authors also have a companion website to the book where they list and dispel some myths regarding the topic:
MYTH: The growth in violent video game sales is linked to the growth in youth violence — especially school violence — throughout the country.
FACT: Video game popularity and real-world youth violence have been moving in opposite directions. Violent juvenile crime in the United States reached a peak in 1993 and has been declining ever since. School violence has also gone down. Between 1994 and 2001, arrests for murder, forcible rape, robbery and aggravated assaults fell 44 percent, resulting in the lowest juvenile arrest rate for violent crimes since 1983. Murder arrests, which reached a high of 3,800 in 1993, plummeted to 1400 by 2001.