The last few years I’ve come across a number of discussions of autism for a couple reasons. First, because my wife was getting a masters degree in speech & language pathology, and SLPs often work with kids who exhibit somewhere along the autism spectrum, so she had to study autism and we’d talk about it. And now we’ve got ourselves a new baby and so we’re approaching the onset of the standard vaccination schedule, and you can’t help but run across folks who talk about the connection between vaccinations and autism. Well, this article doesn’t really address that issue of what causes autism (though I should mention that basically all the reliable evidence shows that there is no vaccination-autism connection whatsoever), but it’s interesting. At least I think so.

Medpage today reviews an article in Pediatrics:

MADISON, Wis. April 4 – An apparent increase over the past decade in the prevalence of children labeled as autistic in special education programs may be a phantom conjured by diagnostic substitution, according to an investigator here.

“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,” said Paul T. Shattuck Ph.D., MSSW, a pediatrics researcher at the University of Wisconsin

“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,” Dr. Shattuck added. He outlined his case for the rise in autism being due largely to diagnostic substitution in the April issue of *Pediatrics.*

His findings suggested that those who seek evidence of an increased incidence and prevalence of autism can’t rely on special education’s trends to support their claims, “because states don’t all use a standard definition of autism, and there is considerable variability in classification of children into special education programs,” Dr. Shattuck wrote.

He designed his study to determine whether the increase in the administrative prevalence of autism (i.e., prevalence as reported by various educational systems versus population-based surveillance) was accompanied by decreases in other diagnostic categories.

To do this, he conducted multiple analyses using data on children classified as having autism in special education programs beginning in 1994, after a new autism-reporting category mandated by the Individuals with Disabilities Education Act was implemented in all but two states (those two, Massachusetts and Iowa, were excluded from the analysis).

He also drew on data published by the U.S. Department of Education on annual state-by-state counts of children ages six to 11 with disabilities in special education from 1984 to 2003.

He found that the average administrative prevalence of autism among children increased from 0.6 per 1,000 to 3.1 per 1,000 from 1994 to 2003.

During the same period, however, in all but five states the prevalence of mental retardation declined by 2.8 per 1,000, and the prevalence of learning disabilities dropped by 8.3 per 1,000. The declines in these two categories occurred despite the fact that from 1984 to 1993 there had been a level or gradual upward trend in each of the categories.

Additionally, the quality of the data was questionable, as suggested by the fact that “changes in the special education prevalence of autism varied tremendously among states despite a common federal mandate to create a separate special education reporting category for children with autism,” Dr. Shattuck wrote.

Of note was the fact that as of 2003, the special education prevalence of autism was within the range of recent population-based estimates in only 17 states.

“The mean administrative prevalence of autism in U.S. special education among children ages six to 11 in 1994 was only 0.6 per 1,000, less than one-fifth of the lowest CDC estimate from Atlanta (based on surveillance data from 1996),” he commented. “Therefore, special education counts of children with autism in the early 1990s were dramatic underestimates of population prevalence and really had nowhere to go but up.”

Dr. Shattuck also noted that some critics have used California as an example to refute the diagnostic substitution hypothesis, because in that state’s social services system the increase in the prevalence of autism has not been accompanied by a change in the prevalence of mental retardation.

“California’s special education and state service trends seem to mirror one
another, thereby suggesting that California’s experience has not been typical of the rest of the country,” he wrote. “This finding does not minimize or invalidate what may actually be a very troubling pattern of change in California that merits additional study and intervention. However, the implications for national policy are clear: California’s changes are unique and should not be the foundation for nationwide policy responses.”

Catherine Lord, Ph.D., an authority on autism at the University of Michigan’s Center for Human Growth and Development, who was not involved in the study, commented that 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.”

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