How prevalent is autism, actually?

How did the CDC calculate its 1-in-68 number?

The CDC computed the 1-in-68 statistic using what is called the Autism and Developmental Disabilities Monitoring (ADDM) Network. Importantly, CDC’s approach accounts for individuals who are not formally diagnosed. Thus, the 1-in-68 figure is indicative of the “true” prevalence, rather than official diagnoses. Taking this approach is crucial because it corrects for children who may not be diagnosed because of family circumstances (i.e. parents who do not accept that their child is different, or parents who are not involved enough to notice that their child is different).

  • Phoenix, AZ
  • Salt Lake City, UT
  • Denver, CO
  • St. Louis, MO
  • Southeastern Wisconsin (including Milwaukee and Madison)
  • The entire state of Arkansas
  • Northeastern Alabama (including Birmingham and Huntsville)
  • Atlanta, GA
  • Central North Carolina (including Raleigh-Durham-Chapel Hill and Greensboro-High Point-Winston-Salem)
  • Baltimore, MD
  • Northeastern NJ (Greater New York City)
  • Pennsylvania*
  • South Carolina*
  • Florida*

What are the caveats with CDC’s numbers?

The ADDM is not meant to be representative

What are the reasons that autism in general might be different than reported by the CDC?

The answer to this lies in how “representative” of a US sample the 12 ADDM sites are. If the selected sites have disproportionately high levels of factors that are correlated with autism (e.g. more skilled workforce, different ethnic background, better socioeconomic measures, etc.), then autism rates would be overstated. This is analogous to measuring sickness levels by visiting hospitals instead of households. On the other hand, the opposite argument is true: the CDC rate would be understated if the ADDM sites happen to be places where autistic children happen not to live.

The final verdict

My best guess is that the CDC rates are actually slightly overstated. In other words, the 1-in-68 number is likely to be more like 1-in-75. The primary reason is that, for an ADDM site to be established, there must be enough autism awareness in the community to put forth sufficient resources.

Other interesting facts

Autism prevalence is rising, but CDC’s figures are based on 8-year-olds in 2010. This suggests that the current prevalence among younger children is much, much higher

Source

  1. CDC’s 2014 Report: http://www.cdc.gov/ncbddd/autism/states/comm_report_autism_2014.pdf

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