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Prevalence of Austism
Autism is rare, yet its prevalence rate makes it the third most common developmental disorder. The most cited statistic is that autism occurs in 4.5 out of 10,000 live births (Stone & Ousley, 1996). This figure is based on large-scale surveys conducted in the United States and England. However, other recent studies have found substantially higher prevalence rates, ranging from 10 to 15 persons with autism per 10,000; this suggests that autism may be more common than previously thought (Gillingham, 1997). In addition, the estimate of children having autism-like behaviors is 15 to 20 out of 10,000 (Van Bourgondien, 1987). Interestingly, estimates on the prevalence of autism vary considerably depending on the country studied, ranging from 2 out of 10,000 in Germany to as high as 16 out of 10,000 in Japan. Possible reasons for the discrepancy in prevalence rates include differing diagnostic criteria, genetic factors, and/or environmental influences.
Autism is four times more likely to affect males than females (Stone & Ousley, 1996). Gender ratios seem to differ as a function of intellectual ratio, with a higher percentage of females found at lower intellectual levels. This gender difference is not unique to autism, since many developmental disabilities have a greater male to female ratio.
Autism appears to be distributed equally among all social classes. Early work with this disorder led researchers to believe that it appeared more often in families of upper social status. This hypothesis has since been disproved. Investigators began to realize that upper class families were simply more likely to have the resources necessary to pay for programs providing diagnoses. Recent trends toward increased recognition of autism and wider availability of public funding for services have led to greater assistance for families at lower social and income levels.
