Epidemiologic surveys of autism have now been carried out in several countries. Methodologic differences in case-definition and case-finding procedures make between-survey comparisons difficult to perform. In spite of these differences, some common characteristics of autism and PDDs in population surveys have emerged with some consistency. Autism is associated with mental retardation and is overrepresented in males (with a male:female ratio of 4.4:1). Autism is found in association with some rare and genetically determined medical conditions, such as tuberous sclerosis. Autism is found in all social classes. The little evidence that exists does not support the hypothesis of secular changes in the incidence of autism, but power to examine and detect time trends is seriously limited in existing datasets. The debate has been largely confounded by a confusion between prevalence and incidence. Although it appears that prevalence estimates have gone up over time, this increase most likely represents changes in the concepts, definitions, and awareness of autism spectrum disorders in both the lay and professional public. To assess whether the incidence has also increased, method factors that account for an important proportion of the variability in rates must be tightly controlled. Taking 10/10,000 as the base rate for autism, a conservative rate of 27.5/10,000 for the combination of all PDDs can be derived. It could well be that, because these surveys were not focusing primarily on the nonautistic group, the actual rate of combined PDDs could be even higher, in the neighborhood of 60/10,000 to 70/10,000, as suggested by three recent surveys.
|Original language||English (US)|
|Title of host publication||The Neurobiology of Autism|
|Publisher||The Johns Hopkins University Press|
|Number of pages||20|
|State||Published - Dec 1 2005|
ASJC Scopus subject areas
- Social Sciences(all)