"Some psychological studies have highlighted the 'addictive' nature of computer games and suggested that they could potentially exacerbate aggressive or anti-social behaviour. However other research claims the reverse - that computer games are a safe outlet for aggression and pent-up emotions."
This can be seen quite clearly by examining the DOJ website that tracks violent crime rates. You can see that children and young teens all over America had a lot of pent up frustrations (probably from trying to rescue that princess in Super Mario Brother I, II, and III). Mortal Kombat was released and violent crime has been declining ever since, thanks to such stress relievers as GTA and the Doom series.
So remember this holiday season to make sure there are at least a few extremely violent video games under that tree. It all comes back for the good of society.
On the serious side, the research done by Alice Mitchell and Carol Savill-Smith does look interesting, and is available for free. I've requested a copy, and if it comes electronically, I can send it out to anybody interested.