Prevalence of autism spectrum disorders in children: A review of international population-based studies using DSM-IV or ICD-10 criteria

This study reviews international population-based studies published from 1997 to 2011 on the prevalence of autistic disorder (AUT) and autism spectrum disorders (ASDs) in children. To minimize the heterogeneous diagnostic criteria and case ascertainment, only population-based studies that adopted DSM-IV, ICD-10, and/or comparable diagnostic systems (e.g., Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule) were included. Point estimates and their 95% confidence intervals were grouped by geographical region and ordered by approximate median birth year for studies that had a population size >=3000 as these studies provide a more precise estimate of prevalence. Overall, the medians of reported ASD prevalence per 1,000 are 6.7-7.8 in North America, 3.6 in Scandinavia, 4.4 in Europe, 6.4-8.6 in Asia, and 1.8-3.9 in Australia. Median AUT prevalence estimates, per 1,000, in the reviewed studies are 1.5 in North America, 1.1-1.2 in Scandinavia, 2.2 in Europe, and 3.0-3.7 in Asia. Prevalence increases in more recent birth cohorts, and in older children, with several studies indicating an ASD prevalence of approximately 1% of children. Evidence suggests that the increase of prevalence worldwide, both in ASD and in AUT, is possibly due to multiple factors such as identification improvements related to the development of available services, professional and public awareness, diagnostic practice, and early identification, as well as possible unexplained increase in risk, rather than to the broadened diagnostic criteria.