Autism appears in 1 percent of children and is four to five times more common in boys than girls, a government review of health and educational records indicates, suggesting that the diagnosis is far more common that previously recognized.

The findings, reported in the Center for Disease Control and Prevention’s Morbidity and Mortality Weekly Report, represent a significant increase from the government’s previous prevalence estimate of 1 in 150, though the rise was expected.

Earlier this year, a report conducted jointly by the CDC and the Health Resources and Services Administration found that autism occurred in 1 in 91 children. That report, however, was based on a telephone survey of parents. The new CDC study is considered more reliable because it’s based on 2006 health and educational records of 8-year-olds in 11 communities across the country.

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The previous CDC estimate of 1 in 150 was based on an earlier version of the study on 8-year-olds.

The current research finds that communities saw an average increase of 57 percent in the number of children diagnosed with autism between 2002 and 2006.

Further, the research shows autism occuring in 1 in 70 boys and 1 in 315 girls.

It is unclear why the increase in diagnosis is occuring, but some of the rise can be attributed to better awareness of the disorder, researchers say.