Autism Prevalence May Not Be IncreasingA number of studies from the United States have found increased rates of autism spectrum disorder (ASD). With a 10-fold increase in ASD prevalence from the 1970s and the 1990s, some have declared that this is an “autism epidemic.” A new study from Sweden investigated whether the so-called autism epidemic has merit. The researchers hypothesized that increasing awareness of the disorder and broader diagnostic criteria, among other factors, may be the cause of increased autism prevalence. The study demonstrates that rather than an epidemic, the way autism is diagnosed and recorded is likely to blame for increased autism prevalence.

The researchers compared two sets of data. The first set came from the Swedish national patient register. The researchers gathered information on over one million children born between 1992 and 2002. The register contains statistics on which children have an official diagnosis of ASD. The second set of data came from the Child and Adolescent Twin Study in Sweden (CATSS). In this study, twins’ parents were interviewed by phone with the Autism-Tics, ADHD, and other Comorbidities inventory. This inventory focuses on the symptoms of ASD.

The Swedish national patient register and the CATSS had different rates of ASD prevalence. The Swedish national patient register data had a population prevalence of ASD at 0.42 percent (with a range of 0.23 percent to 0.60 percent). The CATSS data had a population prevalence of 0.95 percent (with a range of 0.52 percent to 1.59 percent). The prevalence over time was also different between the two data sets. The Swedish national patient register had a linear increase in prevalence over the 10-year period, while the prevalence of undiagnosed ASD symptoms in CATSS was stable over time.

The data suggest that the increase in cases of ASD in recent years could be the result of the way autism is diagnosed and recorded. The findings indicate that there is not an epidemic of autism, but rather, clinicians have become better at identifying autism.

This research is published in the British Medical Journal.

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