Do video games make people violent?

More than 200 academics have signed an open letter criticising controversial new research suggesting a link between violent video games and aggression.

The findings were released by the American Psychological Association.

It set up a taskforce that reviewed hundreds of studies and papers published between 2005 and 2013.

The American Psychological Association concluded while there was "no single risk factor" to blame for aggression, violent video games did contribute.

"The research demonstrates a consistent relation between violent video game use and increases in aggressive behaviour, aggressive cognitions and aggressive affect, and decreases in pro-social behaviour, empathy and sensitivity to aggression," said the report.

"It is the accumulation of risk factors that tends to lead to aggressive or violent behaviour. The research reviewed here demonstrates that violent video game use is one such risk factor."

However, a large group of academics said they felt the methodology of the research was deeply flawed as a significant part of material included in the study had not been subjected to peer review.

"I fully acknowledge that exposure to repeated violence may have short-term effects - you would be a fool to deny that - but the long-term consequences of crime and actual violent behaviour, there is just no evidence linking violent video games with that," Dr Mark Coulson, associate professor of psychology at Middlesex University and one of the signatories of the letter told the BBC.

"If you play three hours of Call of Duty you might feel a little bit pumped, but you are not going to go out and mug someone."

The question about whether violent games inspire violent behaviour "in real life" is a subject that strongly divides opinion.

Why is it so controversial?

While many people play violent video games, few become violent.

The playing of violent video games is often cited as a factor in motivating shockingly violent youth crimes such as high school shootings in the US.

One of the students who carried out the Columbine High School massacre in 1999 used a gun he called "Arlene" - allegedly after a character in a novel inspired by the computer game Doom.

However, most people who played graphically violent games (such as Call of Duty, Hitman, Mortal Kombat) did not resort to violence - and most video games were not violent, said Dr Richard Wilson from trade body Tiga.

"I wouldn't rubbish the [APA] report, but think it is important to look beyond the headline," he said.

"Although there are adult games, there are also adult films, books, TV shows... the content should be, and is, regulated to ensure children and minors do not play inappropriate material."

Does this new work prove playing violent games can result in violent crime?

The Call of Duty franchise has sold over 140 million copies worldwide.

The taskforce said more research was now needed to establish whether violent games did lead to violent criminal behaviour.

However, the group of 230 academics from universities around the world wrote in its open letter to the APA youth violence in the US and around the world was currently "at a 40-year low".

"This decline in societal violence is in conflict with claims that violent video games and interactive media are important public health concerns," they wrote.

"The statistical data are simply not bearing out this concern and should not be ignored."

A study released by the Oxford Internet Institute last year suggested frustration at being unable to play a game was more likely to bring out aggressive behaviour than the content of the game itself.

"We focused on the motives of people who play electronic games and found players have a psychological need to come out on top when playing," said Dr Andrew Przybylski at the time.

"If players feel thwarted by the controls or the design of the game, they can wind up feeling aggressive.

"This need to master the game was far more significant than whether the game contained violent material."

But aren't the ratings designed to protect young people?

Extra parental control would be no match for savvy young gamers, experts argue

In Europe, games are given age-related ratings in accordance with the Pan-European Game Information (Pegi) system.

There are five age ratings - three, seven, 12, 16 and 18.

The problem is that violence is hard to classify.

A Pegi 18 certificate may contain scenes of "gross violence", says the website.

"Gross violence is the most difficult to define since it can be very subjective in many cases, but in general terms it can be classed as the depictions of violence that would make the viewer feel a sense of revulsion," it says.

The APA is calling for extra in-game controls in addition to the current ratings.

"This is censorship by another route," said Dr Coulson.

"The worry I have is that any soft-coded censorship will be immediately subverted.

"The people playing these games are more competent than the people acting as gatekeepers.

"It's kind of putting forward a solution to a problem I don't think exists."

How was the APA research conducted?

The APA taskforce used meta-analysis - combining the results of lots of studies in order to look for patterns and correlations, rather than carrying out any new research itself.

It conducted a comprehensive review of academic work around the subject, some of which dated back to 2005.

"While there is some variation among the individual studies, a strong and consistent general pattern has emerged from many years of research that provides confidence in our general conclusions," said task force chairman Mark Appelbaum.

However, this approach was criticised by the group of experts, which said such correlations sometimes had other explanations.

For example, boys were more likely to play video games than girls but they were also more likely to be aggressive in general.

Dr Coulson also cautioned about work included in the study that may not have been subject to peer review, where it is critiqued by the wider academic community.

"Obviously there is a lot of stuff out there that doesn't get into peer review journals," he said.

"If you look at all the literature in this area you are bound to get a sensationalist conclusion."