The Epidemiology of Autism Spectrum Disorders

Epidemiological studies of pervasive developmental disorders (PDD) have accumulated recently and their results will be reviewed in this lecture. The design, sample characteristics of 40 surveys published between 1966 and 2003 will be described. Recent surveys suggest that the rate for all forms of PDDs are at least 30/10,000 but newer well-designed surveys now suggest that the estimate might be as high as 60-70/10,000.

The rate for Asperger disorder is not well established, and a preliminary conservative figure is 2.5/10,000. Childhood disintegrative disorder is extremely rare with a pooled estimate across studies of  0.2/10,000. A detailed discussion of the possible interpretations of trends over time in prevalence rates will be provided. There is evidence that changes in case definition, improved awareness and new policies in special education services explain much of the upward trend of rates in recent decades.

However, available epidemiological surveys do not provide an adequate test of the hypothesis of a changing incidence of PDDs.  Cluster reports and the few studies where incidence rates have been reported will also be examined. Although many questions remain unanswered with existing data, clear conclusions can be drawn regarding the need to develop more  services for individuals suffering from a PDD.