Despite the increase in reported prevalence of autism spectrum disorder, there is no direct evidence that this corresponds to an increase in the prevalence of the autism phenotype—that is, the symptoms on which the diagnostic criteria are based. This is due to several factors.
Firstly, the increase in the prevalence was reported during a period of repeated modifications and often broadening of diagnostic criteria, which clearly affects the reported prevalence. Secondly, increasing awareness of autism spectrum disorder is associated with diagnostic substitution across categories. It has been estimated that one third of the prevalence increase of autism spectrum disorder between 1996 and 2004 could be attributed to diagnostic substitution, and the increase in autism spectrum disorder has been suggested to parallel a decrease in learning disabilities and mental retardation. Thirdly, prevalence is also sensitive to referral patterns and availability of services. Finally, methodological differences in case ascertainment and assessment alter prevalence—for instance, the availability of, and discrepancies within, official records give rise to large variations between measured and actual prevalence in similar geographical regions. Consequently, the reported increase in prevalence of autism spectrum disorder remains difficult to interpret. Determining if the prevalence is actually increasing has major public health implications, such as in the allocation of adequate health resources and research efforts to find the causes of autism spectrum disorder.
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The GLP aggregated and excerpted this blog/article to reflect the diversity of news, opinion and analysis. Read full, original post: Autism phenotype versus registered diagnosis in Swedish children: prevalence trends over 10 years in general population samples
