Autism Prevalence

One of the most frequently asked questions about Autism Spectrum Disorders is why there seems to be such a large increase in the number of children receiving these diagnoses. Several decades ago we referred to these disorders as rare, and estimated that perhaps 1 in every 10,000 births resulted in autism. Today, the prevalence rate is thought to be as high as 1 in every 150 births (Hughes, 2008). Why this change?

One recent study sought to answer this question by looking at the diagnoses of children in British Columbia and how their diagnoses changed over time (Coo et al., 2008). Unlike some previous studies which tracked diagnoses in groups of children, this study followed each individual child's diagnosis between 1996 and 2004. They found that a large number of these children had their diagnosis changed from another special education designation (for example, learning disability) to autism over this time period. In fact, this switching of diagnosis accounted for at least 1/3 of the increase in the diagnosis during this period of time.

This study suggests that some - but not all - of the increase in prevalence could be the result of changes in diagnostic practices, rather than an actual increase in the number of children with autism.

Reference:

Coo, H., Ouellette-Kuntz, H., Lloyd, J., Kasmara, L., Holden, J., & Lewis, M. (2008). Trends in autism prevalence: Diagnostic substitution revisited. Journal of Autism and Developmental Disorders, 38(6), 1036-1046.

Hughes, J. R. (2008). A review of recent reports on autism: 1000 studies published in 2007. Epilepsy & Behavior, 13(3), 425-437.