The present study asked 100,000 parents across the country a range of health questions, including whether their child had been diagnosed on the autism spectrum and whether he or she currently had the diagnosis. The autism spectrum includes autism, the most severe form, as well as Asperger's syndrome and pervasive developmental disorder-not otherwise specified (PDD-NOS).
The study looked at children ages 6-17 and was based on parent reports, while last year's study looked at 8-year-olds whose diagnosis was noted in school district or other official records.
The fact that the new study found such high rates implies that "there will likely be more demand for (autism-related) services than we had previously thought," said study author Stephen J. Blumberg, a senior scientist at the National Center for Health Statistics.
The new study, like most others, found that boys are four times more likely to have autism than girls.
The parents' answers to the two survey questions also suggests that 15% to 20% of children who were once diagnosed with autism no longer have the condition. Blumberg said the study cannot say whether they lost the diagnosis because they outgrew the condition, or because they were misdiagnosed in the first place.
The higher numbers recorded in the new study suggest that officials are getting better at counting kids with autism – not that more have the condition, several experts said.
"I don't see any evidence that there's a true increase in the prevalence of autism," said Roy Richard Grinker, a professor of anthropology at George Washington University, Washington, D.C.
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