One of the hottest current issues in the field of autism is the reported increase in the incidence and prevalence of the disorder. Over the past several years, a truly dramatic increase in the number of children diagnosed with autism has been reported worldwide. Clinicians, the educational community, speech and language specialists, and developmental-disabilities service agencies as well as epidemiological studies have reported this increase.1 In the 1960s and 1970s, epidemiological studies reported an incidence of autism of four to five cases per 10,000 births. This increased in the 1980s to 2.5 to 16 cases per 10,000, and in the 1990s to five to 31 cases per 10,000. In 2004, one routinely read incidence reports claiming 50 to 67 cases per 10,000. The California State Department of Developmental Services (one of the few state agencies to report such extensive data) found that between 1988 and 1998 there was a 610 percent increase in autism cases. In April 2002, a congressional hearing declared autism a national health emergency. It is estimated that today autism affects as many as 1,500,000 individuals in the U.S. and is rising at an annual rate of 10 to 17 percent. These statistics are indeed staggering.
The fact that the number of children being diagnosed with autism is on the rise is undisputed. However, is there indeed such a large increase in the incidence of autism? Could the increased incidence be the result of increased reporting, perhaps due to greater awareness, better diagnostic tools, and broader diagnostic criteria?
One likely contributor to the increased incidence of autism is the fact that, unlike in the past, money and services are now available for treating autistic children. To understand how diagnoses "follow" resources, let's take a look at what has happened in California. When I first started studying autism as an undergraduate at the University of California at Los Angeles in the late 1960s, the educational system in California provided special classrooms for children with mental retardation and for children with various physical disabilities, but not for children with autism. Understandably, this led parents to actively "shop" for specific diagnoses that would enable their children to receive the best services. And it is likely that professionals were lenient about using the mental retardation diagnosis, knowing that this diagnosis would increase the likelihood the child would receive special services.
The situation changed greatly when, in 1975, special education programs were mandated for children with autism. Largely as a result of parent advocacy and lobbying at various government agencies, as well as lawsuits filed by parents, more and more money was earmarked for autism services. Over time, an autism diagnosis came to be preferred because it was less stigmatizing and yielded more intensive and appropriate services than did a diagnosis of mental retardation.
This shift in the preferred diagnosis shows up clearly in the data: A study in California found that the increase in incidence reported for children with autism was accompanied by a concomitant decrease in reported cases of children with mental retardation. Specifically, the incidence of autism increased by 9.1 per 10,000, whereas the incidence of mental retardation of unknown cause declined by 9.3 per 10,000.2
A recent review of many epidemiological studies conducted in several countries indicates that what happened in California may not be uncommon. The review concluded that the increase in autism is likely due to changes in the concepts, definitions, and awareness of both the lay and professional public—not to an actual increase in the occurrence of autism.3 But the results of that review were not definitive. It may also be that some of the reported increase is due to some actual growth in autism. For example, some researchers believe that the increased incidence is, at least in part, due to increased environmental toxins. It may be that more recent environmental pollutants serve to interact with genetic or other organic propensities, with the result that more individuals develop autism. As in all areas of this mysterious disorder, there is much research yet to be done.
Laura Schreibman is distinguished professor of psychology and director of the Autism Research Program at the University of California at San Diego.
1. Filipek, P.A., Accardo, P.J., Baranek, G.T. et al. (1999). "The Screening and Diagnosis of Autistic Spectrum Disorders," Journal of Autism and Developmental Disorders, 29, 439–484.
2. Croen, L.A., Grether, J.K., Hoogstrate, J., and Selvin, S. (2002). "The Changing Prevalence of Autism in California," Journal of Autism and Developmental Disorders, 32, 207–215.
3. Fombonne, E. (2003). "Epidemiological surveys of Autism and Other Pervasive Developmental Disorders: An Update," Journal of Autism and Developmental Disorders, 33, 365–382.
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