New Estimate of Autism Prevalence from the CDC

The CDC issued a new report presenting surveillance data from the ADDM network. The data, which was also published in this article, puts the rate of autism among 8-year-old US children born in 1998 at 0.9%. This is a significant increase over the previous report from the ADDM network, which looked at children born in 1992 and 1994. At sites which collected data both in 2002 (for children born 1994) and in 2006 (for children born 1998) there was a 57% increase in prevalence during this period.

More Data from California

The California Department of Developmental Services has more data available on their website. These include monthly caseload data, and comparing those to the autism caseload and to the total population of California might provide some interesting insights. For example, we may note that the total caseload of DDS as of April 2009 is 202,924. This compares to a total California population of approximately 38 million, so about 1 in 187 Californians currently receive DDS services. In December 2001 the DDS caseload was 154,862 and the population of California was about 35 million. Thus about 1 in 226 Californians received DDS services in 2001.

California Data

One of the main reasons why many people believe there has been a significant increase in autism are the data of the California Department of Developmental Services. A document worth examining in this context is the report on changes in the California caseload.

Agreements and Disagreements

Reviewing the literature, there are several facts that everyone seems to agree on. Diagnoses of autism have steadily increased since the early 1990's. The definition of autism is now broader than it was in the early 1990's. Autism awareness has significantly increased during this period.

There is no agreement on the reasons for these changes. Let's review some recent research.


Hertz-Picciotto I, Delwiche L. The Rise in Autism and the Role of Age at Diagnosis. Epidemiology. 20(1):84-90, January 2009
Using data from California, the authors argue that "younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases." The autors attempt to calculate the increse that is likely explained by each of the above factors, concluding that the total of all these factors would be insufficient to explain the overall rise in diagnosed autism.


Morton Ann Gernsbacher, Michelle Dawson, and H. Hill Goldsmith, Three Reasons Not to Believe in an Autism Epidemic; Current Directions in Psychological Science. 2005 14(2)
The autors list a number of factors that have contributed to the autism diagnosis increase. They do not attempt to quantify the contribution of each factor.


Bishop DV, Whitehouse AJ, Watt HJ, Line EA. Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder. Dev Med Child Neurol. 2008 Mar 31
The autors provide evidence for diagnostic substitution by examining a sample of 38 adults with a history of developmental language disorder. They conclude that 12 of these patients would "nowadays be diagnosed unambiguously with autistic disorder."


Paul T. Shattuck. The Contribution of Diagnostic Substitution to the Growing Administrative Prevalence of Autism in US Special Education. PEDIATRICS Vol. 117 No. 4 April 2006, pp. 1028-1037
The author presents evidence of diagnostic substitution in special education data. He further argues that "prevalence findings from special education data do not support the claim of an autism epidemic because the administrative prevalence figures for most states are well below epidemiological estimates."

More articles to review...

Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children: confirmation of high prevalence. Am J Psychiatry. 2005 Jun;162(6):1133-41.

Fombonne E. Epidemiology of autistic disorder and other pervasive developmental disorders. J Clin Psychiatry. 2005;66 Suppl 10:3-8.Click here to read

Jick H, Kaye JA. Epidemiology and possible causes of autism. Pharmacotherapy. 2003 Dec;23(12):1524-30.

Rutter M. Incidence of autism spectrum disorders: changes over time and their meaning. Acta Paediatr. 2005 Jan;94(1):2-15.Click here to read

Taylor B. Vaccines and the changing epidemiology of autism. Child Care Health Dev. 2006 Sep;32(5):511-9.