SHOOT-’EM-UP video games increase aggressive behaviour in children and adolescents in the short and long term, according to an analysis of 20 years of research.

Gamers are rated as more hostile by their teachers, are more likely to argue with authority figures and are more likely to be involved in altercations with other students at school. They also tend to perform more poorly on academic tasks.

The analysis comes as a mother condemned the British makers of a game in which players act as bullies. On Thursday, Giselle Pakeerah, who blames the murder of her son on a violent video game, called for the game to be banned.

Researchers from Saint Leo University, in Florida, told the American Psychological Association’s annual conference yesterday, in Washington, that young people who played violent video games — even for a short period — showed an increase in aggressive behaviour afterwards.

Boys, who tend to play games for longer than girls, are particularly at risk. They are often exposed to imagery portraying women as subordinate. But girls who play violent games also demonstrate aggressive behaviour. After playing they prefer to interact with aggressive toys and are more aggressive when interacting with other children.

Kevin Kieffer, one of the researchers, said that players of violent video games “tend to imitate the moves that they just acted out in the game they played”. Children who play violent karate games on screen then use the same behaviour when playing with friends.

As increasingly violent games are released, this latest support for the long-held theory of a link between video games and violence offers little comfort to parents. Ms Pakeerah has called for tighter controls on games before the release of Bully, which features a pupil beating up classmates.

She claims that the game Manhunt inspired Warren Leblanc to kill her son, Stefan, 14, in a Leicester park last February. Players earn points for killings in the game.

Leblanc has been jailed for life, although Manhunt did not feature in the prosecution case against him. Manhunt and Bully are made by Rockstar Games.

Ms Pakeerah said: “I find it shockingly irresponsible because of bullying, which is in the public eye because of the effect it has on young people’s lives. People have been working very hard to stamp out bullying and now we have a game called Bully. This flags up a very important issue, that the computer games industry is not fully regulated.

“There needs to be an independent watchdog regulating the production of such games.”

Manhunt and Bully are only two of the violent games available. In Grand Theft Auto: San Andreas, also made by Rockstar, players pick up prostitutes and deal in drugs. In Hitman: Blood Money, players shoot people for money. Five US groups last year declared these games among the ten most violent video games ever made.

Dr Kieffer and Jessica Nicoll, the study’s co-author, have called for further long-term studies to examine in detail the effects of video games on children.

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