Old Aspergers data and fudgeing prevalence numbers

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The latest government data shows that autism prevalence is on the rise, but a newly-adopted standard for diagnosing the developmental disorder may be muddying the numbers.

The revised criteria for autism — which some consider more restrictive — require both deficits in social communication and social interaction as well as restricted repetitive behaviors, interests and activities for a diagnosis. However, it also includes anyone who had a previous diagnosis of autism.

Now, for the first time, the Centers for Disease Control and Prevention is factoring the changing definition of autism into its regular tracking of autism prevalence.

Figures released in April show that 1 in 59 children have autism — an increase from reports two years ago that found 1 in 68 children were on the spectrum. However, the latest numbers, which rely on data collected on over 300,000 children who were 8 years old in 2014, are based on the older definition of autism.

In the same report, the CDC then evaluated the children under the newer DSM-5 criteria, finding that 18 percent fewer would qualify for an autism diagnosis. Using the updated definition and also including children who had previously received a diagnosis of autism, 4 percent fewer children were found to have autism.

The goal of doing separate analyses using both definitions was to “really give a direct comparison of the difference in prevalence and characteristics based on those two case definitions,” said Daisy Christensen, an epidemiologist on the surveillance team for the developmental disabilities branch of the CDC.

Going forward, the DSM-5 definition will be the primary criteria used by the CDC’s Autism and Developmental Disabilities Monitoring Network for its biennial tracking of children with autism, though the research will also include those diagnosed under the previous definition, Christensen said. The CDC will release its next evaluation, based on 2016 data, in two years.

While it’s possible that the new criteria for autism diagnosis “might exclude some” children who met only the older definition, it’s more likely that any trends of increase or decrease in prevalence will be influenced more by clinicians adjusting their evaluations to the new definition and other factors, she said.

Tom Frazier, chief science officer for the advocacy organization Autism Speaks, said that the impact of the new definition on autism rates will take years to play out.

Clinicians themselves need to get used to the criteria and applying them, he said. The data will be in a “transitional phase” until DSM-5 is the standard being used universally, Frazier said.

Lord said she expects rates of autism to continue to rise, in part because minority communities are becoming more informed about the disorder and minority children are being diagnosed more often.