Unpacking the complex nature of the autism epidemic

The etiology of autism spectrum disorders is unknown but there are claims of increasing prevalence in many countries. Despite more than a decade of epidemiological investigation, it is still unclear whether the rising trend in prevalence reflects a true increase or changes in diagnostic trends and improvements in case ascertainment. This paper discusses changes in diagnostic criteria, decreasing age at diagnosis, improved case ascertainment, diagnostic substitution, and social and cultural influences on the overall effects on prevalence, including the role of an ASD diagnosis as a gateway to funding. The evidence suggests that the increased prevalence of autism spectrum disorder can be partly supported by each of these factors, but remains largely unquantified due to a variety of other global and local factors. The question of how much of a real increase in prevalence has occurred remains crucially important to understand the classification, epidemiology and etiology of autism spectrum disorders but can only be answered if controlling these other factors.