Editorial – The National Prevalence Rate of Autism: Is 1 in 59 a Reasonable Estimate?

Many in the autism community consider the prevalence rate reported by the Centers for Disease Control and Prevention (CDC) to be a reasonable estimate of the size of the autistic community in the United States. Researchers often cite this national statistic in their grant proposals, usually in the opening paragraph, and many published research studies also refer to this estimate.

The Autism and Developmental Disabilities Monitoring Network, a division of the CDC, is responsible for determining the national autism rate in the United States. This year’s rate, 1 in 59, is the highest ever reported by them. The report was based on data collected in 2014 and involved a review of health and education records of eight-year-olds diagnosed with autism. Similar to earlier reports, the researchers collected data from 11 communities throughout the United States.

In my view, the 1-in-59 rate needs to be viewed as historical data. It would be more accurate to preface all citations of the 1-in-59 statistic as representing the population of eight-year-olds with autism in 2014. Furthermore, parents who are planning a family should not assume that the chances are 1 in 59 (or 1.7%) of having a child with autism. This rate actually applies to the risk in 2006, because the participants in the 2014 survey were born eight years earlier.

As noted above, the 2006 national birthrate of autism was 1 in 59 (or 1.7%). At that time, the reported national statistic regarding eight-year-olds was approximately 1 in 150 (based on the CDC’s 2007 report). The latter statistic indicates that the national birthrate of autism eight years earlier (1994) was 1 in 150 (or 0.67%). Given the logarithmic increases in the prevalence of autism that the CDC has reported over the past 12 years, the birthrate of autism today is undeniably significantly higher than 1.7%.

Also, while one might assume that the 11 communities selected by the CDC represent a cross-section of America, the CDC’s April 26, 2018 press release stated that the reported rate “is not a representative sample of the United States.” Instead, the release stated, the report provides a “detailed look at autism in these specific communities.”

The regional prevalence rates reported by the CDC were based on data from Arizona, Arkansas, Colorado, Georgia, Maryland, Minnesota, Missouri, New Jersey, North Carolina, Tennessee, and Wisconsin. Note that there were no communities on the west coast or in the lower Midwest regions, and only Georgia was included in the southeast. All three of these geographic areas include centers of large populations in the United States.

Regarding minority populations, the CDC noted that the rate of diagnosed autism in black and Hispanic children “is approaching that of white children.” The CDC spokesperson also stated that “autism is still more likely to be identified in white children than in black or Hispanic children.” Regarding sex differences, the National Autistic Society in the United Kingdom published a study in 2015 indicating that females with autism are under-diagnosed, in part because their social and core autistic impairments are often less severe than those of males with autism. Thus, at least three rather large segments of the population in the United States are not properly represented in this national prevalence statistic.

Moreover, the CDC reported a wide range of prevalence rates across regions in the U.S. Interestingly, New Jersey had the highest estimated rate of 1 in 34, and Minnesota had the second highest rate of 1 in 42. These rates are almost 40% and 30% higher, respectively, than the national statistic. If autism truly varies greatly across regions, it would be more appropriate to cite prevalence estimates for each region than to rely on a single national statistic.

As many in the autism community are aware, the official definition of autism was broadened in 2013 by a task force sponsored by the American Psychiatric Association. However, the data from the CDC report was collected one year after the new definition of autism was formalized. Thus, the records from the eight-year-olds were based mostly on the previous diagnostic criteria for autism.

Furthermore, the CDC acknowledged in their press release that there were differences in how these individuals were diagnosed and documented. Thus, the current national estimate of autism, 1 in 59, is not based on the current diagnostic criteria for autism, and more importantly, there was no standard method used to determine whether or not an individual was appropriately diagnosed with autism.

It is important to mention that the 1-in-59 prevalence estimate is inconsistent with another government-funded survey on autism. The National Health Interview Survey (NHIS), which collects information for the U.S. Census Bureau, conducted structured interviews with caregivers to confirm a diagnosis of autism. As described in their 2017 published report, they collected data from 2014 to 2016 on 3- to 17-year-olds with autism spectrum disorder, intellectual disability, and other developmental delays. Regarding autism, NHIS reported a rate of 1 in 44 in 2014—the same year the CDC collected the data for its current report— and a rate of 1 in 37 in 2016.

In summary:

• The CDC report is based on historical data collected in 2014.
• It does not reflect a cross-section of the autism population throughout the U.S.
• It relies on non-standardized collection procedures. It is based on outdated diagnostic criteria.
• It is at odds with the U.S. Census Bureau, another government-funded agency.

Given the magnitude of the decisions that are made based on the CDC’s estimate, these concerns raise significant questions:

• Should local, state, and federal governments rely on this estimate to determine policy as well as funding for autism research and services?
• Should the scientific, medical, and autism communities consider this estimate as relevant today?
• Should countries around the world, many of whom rely upon the CDC’s report to estimate the prevalence of autism in their own countries, accept the estimate unquestioningly?

In short, should we simply concede that this is the best that we can do—or should we have an active dialogue about the national prevalence statistic with representatives from various vested communities and discuss ways to best calculate the present (or very recent) rate of autism? I strongly vote for the latter.

Stephen M. Edelson, Ph.D.
Executive Director, Autism Research Institute

The editorial appeared in Autism Research Review International, Vol. 32, No. 3, 2018