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Rise of autism rates inflated, study says

MILWAUKEE – Despite warnings of a national autism epidemic, there’s little data to substantiate such a claim, according to new research compiled by a University of Wisconsin-Madison scientist.

Indeed, special education figures that are being used to suggest an autism explosion are faulty and confounded, said Paul Shattuck, a researcher at the university’s Waisman Center and author of the study, which appears in today’s issue of the journal Pediatrics.

From 1993 to 2003, statistics compiled by the U.S. Department of Education showed a 657 percent increase in autism across the country – an explosive jump that signaled an epidemic to many.

But Shattuck discovered that, at least in most cases, the numbers are not only misleading but also likely inaccurate. On one hand, they don’t support a dramatic increase in autism prevalence, but on the other, the figures could be underestimating the absolute number of children with the condition.

One of the problems is what researchers call the process of “diagnostic substitution”: While the number of reported autism cases has increased, diagnoses of mental retardation and learning disabilities in schools have correspondingly decreased.

Before the early 1990s, the Department of Education didn’t have an autism classification for children with special needs. Therefore, children who would now be considered autistic were often diagnosed with other disorders, invalidating direct comparisons of data collected from the early 1990s and now.

The study suggests researchers may need to use different sorts of data to accurately quantify the prevalence of autism in this country.

“In public health, we make a distinction between ‘population-based estimates’ and ‘administrative-based estimates’ of the prevalence of any given condition or disease,” Shattuck said.

Population-based estimates are those in which researchers actively go out into a community and make a “no stone left unturned” effort to find every person who has a particular disease or condition.

But data collectors generally opt for a faster route, which is to quantify the number of people who are already enrolled in a system and receiving services for a particular diagnosis.

In the case of special education counts for children with autism, the administrative prevalence is simply the number of students with a primary classification of autism divided by the total number of students in that given region, whether it’s a state, district or county.

This means, among other things, that data collected in this manner often underestimate “the true population prevalence because, for instance, schools do not go out into the community and actively seek out and evaluate all kids for autism,” Shattuck said.