Respectful Insolence: Evidence against an "autism epidemic"RI goes on to quote from an editorial arguing that the data is not sufficient to rule out some increase, even if it is not as enormous as initially thought.
... Shattuck analyzes special education figures that are being used to bolster claims of an autism "epidemic" and finds them wanting. In essence, diagnostic substitution can explain nearly all of the apparent increase of autism as recorded by the number of children receiving special education services. What that means is that children that would have been diagnosed with something else 15-20 years ago are now being diagnosed with autism. Dr. Shattuck starts with an example from a different condition, mental retardation as one of his reasons for suspecting diagnostic substitution as a cause of the perceived "epidemic":...Second, prior research has established a precedent of diagnostic substitution in special education enrollment. From 1976 to 1992 the number of children in the mental retardation (MR) category decreased by 41%, whereas the number in the learning disabilities (LD) category increased 198%. There is considerable evidence that suggests this was because of a growing likelihood that schools would use the LD label for children with mild MR, presumably because a label of LD was increasingly seen as carrying less stigma than MR. Finally, a recent epidemiological study depicted a downward deflection in the incidence trend of other developmental disorders just as the trend for autism made a sharp upturn in the early 1990s, again suggesting the possibility of diagnostic substitution.
I tend to believe the increase is relatively small, and perhaps due to the "silicon valley effect" (mating engineers). I have personal knowledge of two children who have both "educational" and "clinical" (different worlds) diagnoses of autism spectrum disorder. They are remarkably different people with very different IQs and abilities. In some ways they are almost perfect opposites, though they share a few common traits.
This is a superb mess. Much of its driven by an astoundingly boneheaded decision; "mental retardation" does not quality for educational services in most states, "learning disability" or "autism" do. I think the reasoning is supposed to be that "MR" can't be helped by special services, but an assymetric defect or autism can. Not surprisingly psychologists, physicians, teachers, and parents serve the needs of children best by conspiring to make the diagnosis of "mental retardation" relatively rare. Duh.
Other than the "mental retardation services" debacle, the autism classification confusion is perpetuated by our almost complete lack of understanding of what's happening, why it happens, and how it happens in the brains of these children and adults. It's very hard to classify something you truly don't understand. "Dropsy" in the 19th century became everything from venous insufficiency to renal failure to heart failure in the 20th century.
We're gradually moving to an anatomic-functional-genetic classification of brain development disorders. With luck both "autism" and "schizophrenia" will join "dropsy" in the garbage heap of abandoned ontologies. One day we'll be able to make meaningful assignments of individual brains to useful classifications, and then the real research will begin.