WASHINGTON (AP) - The longer young children spend in day care away from their mothers the more likely they are to be overly aggressive by the time they reached kindergarten, according to the largest study of child care and development ever conducted.

The basic results of the 10-year, 10-city federally financed study were outlined at a briefing.

Principal researcher Jay Belsky of Birkbeck College in London was presenting the findings in more detail Thursday in Minneapolis at a meeting of the Society for Research in Child Development.

"There is a constant dose-response relationship between time in care and problem behavior, especially those involving aggression and behavior," Belsky told reporters.

Belsky, a research psychologist who worked at Penn State University until two years ago, added that children who spend more than 30 hours a week in child care "scored higher on items like "gets in lots of fights,' "cruelty,' "explosive behavior,' as well as "talking too much,' "argues a lot,' and "demands a lot of attention.'

"If more time in all sorts of (child care) arrangements is predicting disconcerting outcomes, then if you want to reduce the probability of those outcomes, you reduce the time in care," said Belsky. "Extend parental leave and part-time work."

However, Sarah Friedman of the National Institute of Child Health and Human Development, which financed the study, said the federal agency "is not willing to get into policy recommendations."

One of the lead scientists on the study with Belsky, she said, "The easy solution is to cut the number of hours but that may have implications for the family that may not be beneficial for the development of the children in terms of economics."

The study followed more than 1,364 children in a variety of settings, from care with relatives and nannies to preschool and large day care centers. Its conclusions are based on ratings of the children by their mothers, those caring for them and kindergarten teachers.

The average time in day care for all those studied was 26 hours per week.

Researchers found that 17 percent of the children who were in care for more than 30 hours per week were regarded by teachers, mothers and caregivers as being aggressive toward other children. That compared with 6 percent for the group of children in child care for less than 10 hours a week.

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