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Their conclusions were that children who spend longer than two hours in front of a computer or television screen are more likely to suffer psychological difficulties, regardless of how physically active they are.

The authors of the report, published in the November edition of the American journal Pediatrics, conclude that limiting children's screen time may be important for ensuring children's future health and wellbeing.

According to the activity monitor, the children in the study who spent more time sedentary had better psychological scores overall. Those children who did more moderate physical activity fared better in certain psychological areas, including emotional and peer problems, but fared worse in some areas related to behaviour, including hyperactivity.

Lead author Dr Angie Page from the University of Bristol's Centre for Exercise, Nutrition and Health Sciences said: "Whilst low levels of screen viewing may not be problematic, we cannot rely on physical activity to 'compensate' for long hours of screen viewing.

"Watching TV or playing computer games for more than two hours a day is related to greater psychological difficulties irrespective of how active children are."

Children's psychological wellbeing was assessed on the basis of a strengths and difficulties questionnaire which rated their emotional, peer, conduct and hyperactivity problems.

The children were asked to rate a series of statements as true on a three-point scale, varying from not true, to somewhat true to certainly true. Statements to assess their emotional wellbeing included; 'I am often unhappy, down-hearted or tearful', while statements to assess their peer problems included; 'I am usually on my own', 'I generally play alone or keep to myself'.