UW researcher doubts autism epidemic - But expert says tally of cases may be too low

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Autism epidemic doubted

But expert says tally of cases may be too low

By SUSANNE RUST

srust@...

Posted: April 2, 2006

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.

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Indeed, special education figures that are being used to suggest an autism

explosion are faulty and confounded, said 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% 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, they're 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.

In other words, " special education trends cannot be validly used to

substantiate claims of the presence or absence of an autism epidemic, "

Shattuck said.

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 from the early 1990s and now.

Different ways to count

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. " As you might imagine,

these kinds of studies are difficult to execute and cost a lot of money, "

Shattuck said.

So, 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.

For instance, consider data collected in Wisconsin: In 1992, 18 children

were counted in special education programs as being autistic. By 2002, that

number had jumped to 2,739.

" The conclusion is that the prevalence of autism has grown by 15,117

percent. This is ridiculous, " Shattuck said. " No credible clinician or

scientist in the field would ever suggest there were actually only 18

children with autism in all of Wisconsin in 1992. "

Also consider this: In 2002, there were about 1.3 million children between

the ages of 6 and 21 living in Wisconsin.

" If we assume that true prevalence of autism is about six in every 1,000

children, " an estimate based on smaller, more accurate population-based

evidence analyses, " then we would expect the true number of kids between the

ages of 6 and 21 in Wisconsin with an autism spectrum disorder to be around

7,800 . . . a lot higher than the 2,739 actually identified in special

education that year, " Shattuck said.

Wrong in two ways

In other words, the special education numbers not only discount the fact

that the diagnosis for autism has changed over the years - making yearly

comparisons faulty and inaccurate - but they also underestimate the number

of children who actually have it.

" This is not anything new, " said Glen Sallows, a clinical psychologist and

director of the Wisconsin Early Autism Project, which is based in Madison.

" Other people have been saying the same thing " about diagnostic substitution

for quite a while.

But he suspects this is the first paper that has really proved the case.

" Researchers have pointed out that the definition of autism has changed over

time, " Sallows said. It's now one of 13 categories schools use to classify

children identified as having special needs.

In addition, there are no uniform diagnostic practices or guidelines among

states or school districts. That means how children are classified can vary

dramatically between states and school districts.

Shattuck did discover that California does not follow the pattern he noted

among other states: While autism numbers in the state grew, there was no

corresponding decrease in mental retardation.

This indicates that California should not be considered representative of

the rest of the nation, which it has been in many press reports.

In a commentary that accompanies Shattuck's paper, Craig Newschaffer, an

epidemiologist at the s Hopkins Bloomberg School of Public Health in

Baltimore, wrote that despite the flaws in administrative-prevalence

studies, and the potential for diagnostic substitution, it " remains

difficult to ascribe all the observed autism prevalence increase to this

particular phenomenon. "

But he thinks it will be hard to find data that support or refute an

increase in the disorder in the past two decades. Therefore, he believes

it's time to accept that and instead focus on the causes of autism.

From the April 3, 2006 editions of the Milwaukee Journal Sentinel

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