The latest addition to the CDC Autism and Developmental Disabilities Network study is now out with results discussed here. Prevalence in the U.S. (based on detailed study of six states) was estimated to be as high as 1 in 150 children. The number still seem to be climbing, although dramatic differences exist between states (see Alabama vs. New Jersey below), and some increase could be related to issues of diagnostic substitution or qualifying for services. In New Jersey, the state with the highest prevalence of autism, 97% of diagnosed students were receiving special education services.
When states provided IQ data, significant differences also existed between the percentage of diagnosed ASD students with cognitive impairment (for instance, 33% in Utah vs. 60% in South Carolina).
Answers to the most important questions raised by these data, are sometimes very difficult to answer. The largest prevalence studies usually preclude any detailed clinical information about the various children diagnosed with an autism spectrum disorder, while the detailed clinical studies suffer by their small numbers of children fully assessed.
Interestingly, a recent Taiwanese study in Pediatrics found increased incidence rates for autism, but as in the U.S. other diagnostic categories like mental retardation had decreased. Below is a graph from that study - look at the strange peaked shapes of the curves for diagnosed cases of ADHD and autism. Because the researchers only looked at diagnoses submitted to insurance companies - why did the number of ADHD and autism kids rise and fall? Did they no longer present to their doctor? Did they no longer meet the diagnostic criteria? Hmmm...
Scientific American: Autism More Common in U.S.
Diagnostic Substitution and the Prevalence of Autism abstract only
More Diagnostic Substitution and Autism
The Mislabeled Child in The New Atlantis
Technorati Tags: autism, ADHD, diagnostic substitution