Data provides misleading picture of
autism
by Terry Devitt
Wisconsin Week
University Communications
Posted: April 3, 2006
If statistics compiled by the U.S. Department of Education are to be believed,
in 1992 the state of Illinois had only 322 diagnosed cases of autism among
school children. In 2003, according to the same statistical source, Illinois had
more than 6,000 children diagnosed as autistic.
National special education statistics, which showed a 657 percent increase in
autism over the decade from 1993 to 2003, are routinely used to suggest the
country is experiencing an epidemic of autism, a developmental disorder of
children characterized by impaired social and communication skills as well as
repetitive behaviors and obsessive interests.
But inconsistencies in how the condition is diagnosed throughout the nation's
schools, and the fact that the increasing trend for autism coincides with a
corresponding slump in the reporting of mental retardation and learning
disabilities, challenges the use of special education data to portray a national
epidemic of autism, according to a new study published in the current issue of a
leading medical journal (April 3, 2006).
Shattuck
Paul Shattuck, a researcher at the University of Wisconsin-Madison's Waisman
Center, writing in Pediatrics, says special education data cannot be used to
claim there is an autism epidemic because the figures are "hopelessly
confounded" by changing and uneven identification and reporting practices among
schools and states.
At issue, says Shattuck, is the practice of "diagnostic substitution," where
educators, over time, have increasingly applied the autism label to children
who, in the past, would have been labeled differently.
"My research indicates that the increase in the number of kids with an autism
label in special education is strongly associated with a declining usage of the
mental retardation and learning disabilities labels in special education during
the same period," Shattuck says. "Many of the children now being counted in the
autism category would probably have been counted in the mental retardation or
learning disabilities categories if they were being labeled 10 years ago instead
of today."
The point, says Shattuck, is that identification and diagnostic practices change
over time and can lead to a misperception that a condition is more prevalent
than it has been in the past.
"Each year since 1994, the probability of using the autism label has increased
while there has been a corresponding decrease in the likelihood of educators
using the mental retardation and learning disabilities categories."
In contrast to the dominant pattern, California was found to be one of only a
handful of states where there was no decrease in the number of children labeled
mentally retarded corresponding with an upward trend in identification of
autism. This undermines the use of data coming out of California as a
representative indicator of what is happening in the rest of the country, as has
been suggested in recent press accounts and official reports, Shattuck argues.
In the U.S., federal law mandates the provision of special education in the
nation's schools. Schools are required to provide specialized services to
children identified as having special needs and they must classify individuals
according to 13 specified categories for the sake of annual enrollment reports.
Autism was only added to the list in the early 1990s, and the federal statute's
definition of the condition, amounting to just a few sentences, is vague,
Shattuck says.
What's more, there are no uniform diagnostic practices or guidelines among
states or school districts, meaning that how children are diagnosed and sorted
in special education settings can vary dramatically from school to school.
"Schools nationwide don't adhere to any common diagnostic guidelines when
they're sorting kids into these categories," Shattuck explains. "States and
individual schools are left to devise criteria. Everyone is using a different
yardstick to measure the same thing."
Shattuck notes that the diagnostic methods employed by schools in special
education settings are distinct from medical and psychological diagnoses of
autism, which entail a more precise definition of the condition and uniform
diagnostic methodologies.
Catherine Lord, an expert on autism at the University of Michigan, noted that
the new study has important implications for understanding the link between the
everyday lives of children with autism and the ways the condition is identified
and labeled in schools. "Shattuck's work has both theoretical and practical
importance. It highlights the need to consider the immediate implications for
children's lives of the lag between scientific findings regarding the diagnosis
and prevalence of autism, and state and school system policies," Lord says.
Shattuck emphasized that his study does not show, one way or another, whether
there is an epidemic of autism. His study, he says, only shows that trends from
special education data are insufficient to make such a determination, as is
commonly done.
"The upshot is that it is not valid to conclude there is an epidemic of autism
by looking to special education data, because the special education data is
plagued with this diagnostic substitution phenomenon and the lack of nationally
uniform diagnostic procedures."
Shattuck says his study reveals, among other things, a national inability to
accurately measure the scope of developmental disability among Americans.
"In fact, we simply do not have an adequate infrastructure of public health data
in this country to say one way or another whether the true prevalence of autism
has changed in the general population since the early 1990s. And this study
emphasizes why it is so important to continue funding the longitudinal study of
prevalence in several states, funded by the Centers for Disease Control, that
began recently," he says.
"It is in the absence of good quality information that people understandably
make the mistake of looking to the special education data to draw conclusions.
And I think parents and advocates have every right to be angry at our collective
inability to answer such consequential questions as, 'Do more of our children
have autism than in the past? If yes, then why?' "
Shattuck's research was supported by a grant from the National Institute of
Child Health and Human Development.
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