This upward trend has been driven largely by surges in the number of children found to have autism and attention deficit hyperactivity disorder, although the prevalence of stuttering and learning disabilities has also increased.
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The study, which appears in the June issue of the journal Pediatrics, is the first time nationally representative data on developmental disabilities has been collected since 1988, says Sheree Boulet, Dr.P.H., one of the study's authors and an epidemiologist at the CDC's National Center on Birth Defects and Developmental Disabilities.
The reasons for the increases aren't clear, but growing awareness and increasing acceptance of developmental disabilities have probably played a big role, Boulet says. For instance, she explains, the availability of early and effective treatments for conditions such as ADHD might be encouraging more parents to have their children screened for the disorder.
The study findings are to be expected, given the "increased awareness and much better reporting," says Alan Hilfer, Ph.D., the director of psychology at Maimonides Medical Center, in New York City.