This is a case of torturing the data to make it fit a theory

Guy Cumberbatch, Communications Research Group

The findings show that of children who watch less than an hour of television a day at the age of 14, only 5.7% turned to violence between the ages of 16 and 22.

For those who watch between one and three hours, this jumped to 22.8%.

The rate went up again to 28.8% for those who watched more than three hours a day.

The effect was more evident in boys than in girls.

For girls who watched more than three hours TV a day the proportion who became aggressive after the age of 16 was 12.7%, compared to boys at 45.2%.

Research 'flawed'

However, a British expert said the study findings were "highly misleading".

Guy Cumberbatch from the Birmingham-based Communications Research Group said the data had been "tortured to fit a theory".

He said the relatively small number of children who watched less than one hour a day - 88 out of the 700 - represented an extreme which it was unfair to use as a basis of comparison.

"How many families do you know where children watch this amount or less?" he said.

"These are highly unusual families - the kind who are more likely to be taking their children to art galleries and museums.

"And there are so few of them compared to the rest of the children studied."

Avid viewer

Mr Johnson said the increase in aggressive behaviour associated with higher television viewing held true both for people who had previous violent incidents and for those who had not shown earlier aggression.

That meant the findings were not merely the result of people already prone to violence being more avid viewers.

Mark I Singer of the Case Western Reserve University in Cleveland, Ohio, in 1988 researched behaviour in youths who watched more than six hours of TV a day.

He has welcomed the new report, calling it an important study which covered a significant period of time and took into account outside influences.

He said one of the most important findings was the relationship between the sexes and their television habits and the likelihood of their turning to violence.

In a commentary accompanying the report, Craig A Anderson and Brad J Bushman of Iowa State University said the findings were "important evidence showing that extensive TV viewing among adolescents and young adults is associated with subsequent aggressive acts".

The effects were "not trivial" and suggested it may be worthwhile to restrict the viewing time of adolescents, they added.