Sociological Environmental Causes are Insufficient to Explain Autism Changepoints of Incidence

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Why this study matters!

The Environmental Protection Agency (EPA) recently published a study analyzing time trends in the cumulative incidence of autistic disorder (AD) in the U.S., Denmark, and worldwide. A birth year changepoint (CP) around 1988 was identified. It has been argued that the epidemic rise in autism over the past three decades is partly due to a combination of socio‑ logic factors along with the potential contribution of thimerosal containing vaccines. Our work conducted an expanded analysis of AD changepoints in CA and U.S., and determined whether changepoints in time trends of AD rates temporally coincide with changepoints for the proposed causative sociologic and environmental factors. Birth year changepoints were identi‑ fied for 1980.9 [95% CI, 1978.6-1983.1], 1988.4 [95% CI, 1987.8-1989.0] and 1995.6 [95% CI, 1994.6-1996.6] for CA and U.S. data, confirming and expanding the EPA results. AD birth year changepoints significantly precede the changepoints calculated for indicators of increased social awareness of AD. Furthermore, the 1981 and 1996 AD birth year changepoints don’t co‑ incide with any predicted changepoints based on altered thimerosal content in vaccines nor on revised editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM).


A great deal of attention has been focused on the possibility that sociologic factors account for a significant fraction of the rise in autism. Our work demonstrates that the temporal changes in the rise of autistic disorder do not correspond to temporal changes in sociologic factors such as increased parental and professional awareness, or federal special education funding. Our study does not rule out the pos‑ sibility of sociologic effects artificially elevating AD prevalence after 1996, the latest AD BYr changepoint detected from our datasets. However, our results support and expand the recommendation in the EPA changepoint publication,[13] to place emphasis on iden‑ tifying environmental or other factors that are temporally associated with specific AD BYr CPs of 1981, 1988 and 1996. Further research on other environmental factors is clearly warranted.