There is no question that the incidence and prevalence of autism are on the rise. Starting in the early 1990s and continuing to today, there has been a steady rise in the number of children diagnosed with autism. Prior to 1990 the estimates of autism prevalence were about 3 per 10,000. The most recent estimates from the CDC and elsewhere now have the number at about 100 per 10,000, or 1%.
The burning question is – why are the rates increasing steadily? There are those, particularly in the anti-vaccine community, who conclude that the increase in prevalence is a real biological effect – an epidemic – and is evidence for an environmental cause (which they believe is vaccines, even though the scientific evidence does not support this position). However, the evidence strongly suggests that the rising prevalence of autism is largely an artifact of broadening the diagnosis and increased surveillance.
It should be noted that the data cannot rule out a small true increase in autism prevalence. Some hypothesize that increasing maternal and paternal age are contributing to the incidence of autism, but I will leave that question for another post.
A new study now adds significant support to the surveillance hypothesis – Ka‐Yuet Liu, Marissa King, and Peter S. Bearman from Columbia University, publishing in the American Journal of Sociology, report that the risk of being diagnosed with an autism spectrum disorder (ASD) correlates with social proximity to another family with a child with an ASD diagnosis. For those interested in this topic, the full paper is worth a read. While it gets technical at times, the authors do an excellent job of reviewing this topic in detail.