The following post was made by Adam Dreyfus, Director, Sarah Dooley Center for Autism at St. Joseph’s Villa.
Penn State University researchers have concluded that as much as 65% of the increase in autism rates could be attributed to changing diagnoses, primarily children being moved from the category of Intellectual Disability into the Autism Spectrum category. They postulated that this could be due to the difficulty in drawing clear lines between disorders and the difficulty for assessors in selecting the right diagnosis. “Because features of neurodevelopmental disorders co-occur at such a high rate and there is so much individual variation in autism, diagnosis is greatly complicated, which affects the perceived prevalence of autism and related disorders” said Santhosh Girirajan, assistant professor of biochemistry and molecular biology and of anthropology at Penn State and the leader of the research team. She suggested that, “Standardized diagnostic measures incorporating detailed genetic analysis and periodic follow up should be taken into account in future studies of autism prevalence.”
I’ll say two things here. One, I believe that much of the ‘migration’ into new categories is the result of the fact that a diagnosis of autism can result in more in services being delivered at a higher rate, and two, while I do not argue the findings here, I will say that there are more kids showing up with more variations of autistic spectrum disorder every year and these are not simply students who would have traditionally been classified as intellectually disabled.
Source: Increasing prevalence of autism is due, in part to changing diagnoses (Penn State website)