Is There an Epidemic of Autism?

Abstract

The debate on the hypothesis of a secular increase in rates of autism would benefit from a clear recognition of the methodologic limitations of existing data. No psychiatric case register study has ever allowed for estimating and monitoring the incidence of autistic conditions over time.1Cross-sectional surveys hugely differ in their case definition and case identification methods that account for large variations in prevalence estimates both over time and across areas, precluding a meaningful analysis of time trends. That rates in recent surveys are substantially higher than 30 years ago merely reflects the adoption of a much broader concept of autism, a recognition of autism among normally intelligent subjects, changes in diagnostic criteria, and an improved identification of persons with autism attributable to better services.1,2 The only epidemiologic study where case definition and identification could be held constant failed to detect an increase in rates of autism in successive birth cohorts from 1972 to 1985.3 Most of the claims about the ‘epidemic’ of autism are therefore based on referral statistics from various centers. The report of the Department of Developmental Services from California has been, and still is, widely quoted as evidence for an epidemic of autism.4 The key data of this report (Table 1 and Fig 1) need a critical examination. View this table: Table 1. Autism and Other PDDs Registered in California (1987–1998) Fig. 1. Distribution of birth dates of regional center eligible persons with autism (California). First, the figures apply to numbers rather than …