Comparison of Two Case Definitions for Ascertaining Prevalence of Autism Spectrum Disorder among 8-Year-Old Children.

The Autism and Developmental Disabilities Monitoring (ADDM) Network conducts population-based surveillance of autism spectrum disorder (ASD) in multiple US communities among 8-year-old children. To classify ASD, ADDM sites collected text descriptions of behaviors from medical and educational evaluations which were reviewed and coded by ADDM clinicians. This process took at least four years to publish data from a given surveillance year. In 2018, we developed an alternative case definition utilizing ASD diagnoses or classifications made by community professionals. Using surveillance years 2014 and 2016 data, we compared the new and previous ASD case definitions. Compared to the prevalence based on the previous case definition, the prevalence based on the new case definition was similar for 2014 and slightly lower for 2016. Sex and race/ethnicity prevalence ratios were nearly unchanged. Compared to the previous case definition, the new case definition's sensitivity was 86% and positive predictive value was 89%. The new case definition does not require clinical review and collects about half as much data yielding more timely reporting. It also more directly measures community identification of ASD, thus allowing for more valid comparisons among communities, and reduces resource requirements while retaining similar measurement properties to the previous definition.