Pathological gaming is not simply a 'phase' that most children go through, researchers say. (iStock)

About nine per cent of children and teens play video games so long that it places them at higher risk of anxiety, depression and bad grades, a study suggests.

The researchers defined gaming as pathological when it interferes with everyday life including grades, emotions and relationships — a definition that resembles how gambling addictions are often described.

The study, based on a two-year look at 3,034 children in Grades 3, 4, 7 and 8 in Singapore, found that nine per cent of players were addicted.

Gaming was not merely a symptom of disorders such as depression, anxiety and social phobia, Douglas Gentile, a psychologist at Iowa State University in Ames, and his co-authors said in Monday's issue of the journal Pediatrics.

While previous studies described factors tied to pathological video gaming, the latest research provides data on risk factors for becoming a pathological gamer, how long it lasts, what the outcomes are and whether it is the main problem or simply a symptom.

"Although children who are depressed may retreat into gaming, the gaming increases the depression," said the psychologists and social workers who authored the study.

"Many clinics assume that children may be depressed or anxious and therefore retreat into games as a coping strategy. Our data demonstrate that this assumption is overly simplistic."

In the study, 84 per cent of pathological gamblers were still defined that way two years later, but only one per cent of children became pathological gamers during the same window.

"Therefore, pathological gaming is not simply a 'phase' that most children go through," the researchers said.

Kids who stopped being pathological gamers during the study period showed lower levels of depression, anxiety and social phobia compared with peers who didn't stop, the researchers noted.

The Entertainment Software Association, a trade group, has argued Gentile used an unproven definition of pathological gaming and negatively interpreted small differences in behaviours of problem gamers and other children in the survey.

The American Psychiatric Association is weighing whether to add video game addictions to the fifth edition of its diagnostic manual, due out in May 2013. Another behavioural addiction, pathological gambling, is another proposed addition, a topic with a deeper research base.

The study was supported by a grant from the Ministry of Education and the Media Development Authority of Singapore.