Editorial: The rising prevalence of autism.

The first autism surveys were simple head counts of children already diagnosed with a severe autism phenotype and residing in small, circumscribed geographical areas. Prevalence was low, ranging from 0.4 to 2/1,000 in the 1960's and 1970's. Today, the methodology of surveys has become more complex; studies include large populations, multiple sites, stratified samples and rely on intricate sets of screening activities followed by some form of diagnostic confirmation procedures. Yet, and as surprising as it may be, there is no standardization of autism survey methodology. Each survey has unique design features that reflect the local educational and health services infrastructure and current social policies for children with disabilities, they include or not parents, teachers and subjects with Autism Spectrum Disorder (ASD), and rely on variable screening and diagnostic instruments and methods. As such, prevalence differences between studies are hazardous to evaluate and whether observed discrepancies are due to method factors or true differences in population parameters, cannot be determined.