LOS ANGELES, Oct. 5 (Xinhua) -- Autism among children is more common in the United States than previously thought, a new study shows.

    According to the study, one of every 91 children is affected, a much higher rate than previously estimated in other studies which showed that about one of every 150 children suffered from the disorder.

    The study, published in the October issue of Pediatrics available on Monday, estimates that 110 of every 10,000 U.S. youngsters will be diagnosed at some point in their lives with an autism spectrum disorder. That currently translates to about 673,000 American children with some form of autism.

    In the study, researchers from the U.S. Centers for Disease Control and Prevention and Harvard Medical School examined data from the 2007 National Survey of Children's Health, which included more than 78,000 children from across the country, all between three and 17 years old.

    The findings show that parents of 1,412 children reported that a doctor had given their child a diagnosis of autism spectrum disorder. Only 913 parents, however, said their child currently had an autism spectrum disorder.

    Of that group, 494 parents classified their child's autism as mild, and 320 parents described it as moderate. Just 90 parents said their child's autism was severe.

    The authors also suggested that autism might have been considered during the initial diagnosis of a child but later dropped if the child turned out to have another disorder.

    "We do know that individuals with autism can have a diagnosis early on and then lose that diagnosis, and we don't know the factors that could explain this," said Geraldine Dawson of the autism advocacy group Autism Speaks.

    "Is it having received good, early behavioral intervention? Or, is there a group of kids that have better biological outcomes? Or, it may have something to do with how kids get diagnosed at different ages. Maybe as kids develop, they may not be getting the same kind of evaluations."

    The study also found that the odds of receiving an autism spectrum disorder diagnosis were four times higher for boys than girls, and that non-Hispanic black and multiracial children were less likely to have an autism spectrum disorder than white children.

    Autism spectrum disorders are a group of neurodevelopmental disorders, including autism, Asperger syndrome and pervasive developmental disorder. Severity varies from child to child.

    Characteristic behavior includes impaired social interaction, difficulty with communication and repetitive behaviors. Over a lifetime, health-care costs for someone with autism are estimated to be more than 1.6 million U.S. dollars, according to the study.