Is There a Real Increase in the Incidence of Autism?

Statistics Can Be Confusing

Is there an increase in incidences of autism spectrum disorder (ASD) in the United States? According to a November 2018 study published in the journal Pediatrics:

"Parents of an estimated 1.5 million US children aged 3 to 17 years (2.50%) reported that their child had ever received an ASD diagnosis and currently had the condition...The estimated prevalence of US children with a parent-reported ASD diagnosis is now 1 in 40, with rates of ASD-specific treatment usage varying by children’s sociodemographic and co-occurring conditions."

This number was a significant jump from the one published in November 2015, when the CDC announced that, in 2014, the incidence of autism among children had increased in just one year from 1:68 to 1:45 children. And the CDC study before that suggested that the rate was just 1:80.

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Why Are the Numbers Rising?

Is the rapid increase in the incidence of autism real or apparent? Could ongoing changes in the way autism is described and diagnosed be to blame? This is an ongoing controversy, with strong advocates on both sides—but most people in the scientific community believe that the incredibly fast increase in autism prevalence is, at least in part, a bit of an illusion. Here are just a few reasons why the numbers should be taken with a grain of salt:

  • The CDC reports on the prevalence of autism are based entirely on parent reports and not on medical records. Parents were asked "whether children ever received an ASD diagnosis by a care provider," not whether the diagnosis was verified or whether the child still qualified for the diagnosis.
  • Most of the children whose parents say they have a diagnosis of autism are from relatively wealthy, white, educated, married parents living in a major metropolitan area. These facts suggest a possible cultural or socioeconomic bias in reporting and/or diagnosis.
  • An older Danish study concluded: "Changes in reporting practices can account for most (60%) of the increase in the observed prevalence of ASDs in children born from 1980 through 1991 in Denmark. Hence, the study supports the argument that the apparent increase in ASDs in recent years is in large part attributable to changes in reporting practices."

But on the other hand, there is no question that more and more children do seem to have autism diagnoses. Some researchers say that the issue is not that the numbers are increasing but that more and more people are accurately diagnosing—and the true numbers are finally being revealed.

How and Why Autism Diagnoses First Exploded

Autism was first described as a unique disorder in the 1940s. It was described by Dr. Leo Kanner and included only those children with what might be described today as "severe" or "level 3" autism spectrum disorder.

Up until 1990, autism was not included in legislation aimed at guaranteeing an education to individuals with handicaps. In 1990, the new Individuals with Disabilities Education Act added autism to its list of categories of children and youth served under the act. The new law also added transition services and assistive technologies to its requirements. Autism had never been tracked as an educational statistic before 1990. Since 1990, the incidence of autism in schools has risen dramatically. In 1991, the Autism Diagnostic Interview was published. This was the first generally recognized tool for diagnosing autism.

In 1992, the American Psychiatric Association released the Diagnostic and Statistical Manual (DSM-IV), which refined diagnostic criteria for autistic disorder. Autism became a spectrum disorder; in essence, it became possible for someone to be very autistic or mildly autistic. New diagnoses, including the "high functioning" Asperger syndrome and the "catch-all" PDD-NOS, were added to the manual.
In the early 1990s, with new diagnostic tools and categories available, autism diagnoses began to soar. In the 10 years between 1993 and 2003, the number of American schoolchildren with autism diagnoses increased by over 800%. Between 2000 and 2010, the number went from 1:150 to 1:68.

Why Did Autism Diagnoses Soar?

There are two schools of thought on this issue. On the one hand are those who say that the change in diagnostic criteria, combined with new school statistics and a rising awareness of autism all created an apparent (but not real) epidemic. This theory is almost certainly correct, to at least some degree, but while it may explain a large percentage of the increase it may not explain a more modest increase.

On the other hand, are those who say that some external factor has caused a real increase in the number of individuals who actually have symptoms that are diagnosable with autism. There are many different theories as to what that external factor may be—and (of course) it is possible to correlate the increase in autism diagnoses with an increase in many other things ranging from cell phone use to GMOs to vaccine use. While some of these correlations seem downright silly, others have attracted serious interest from researchers.

Are Autism Diagnoses Still on the Rise?

This question is still up in the air, especially now that the definition of and criteria for diagnosing autism have changed (with the 2013 publication of the DSM-5). There are many different perspectives on what is likely to happen with the new criteria. Some experts expected a decline in autism diagnoses now that Asperger's syndrome and PDD-NOS are no longer available as "catch-all" options. Others expected an increase, as awareness and services improve. At this point, it's still unclear as to what the new diagnostic criteria will do, but it is clear that the number of parents reporting children who have been diagnosed by someone, at some time, continues to rise.

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  1. Kogan MD, Vladutiu CJ, Schieve LA, et al. The Prevalence of Parent-Reported Autism Spectrum Disorder Among US Children. Pediatrics. 2018.

  2. Hansen SN, Schendel DE, Parner ET. Explaining the Increase in the Prevalence of Autism Spectrum Disorders: The Proportion Attributable to Changes in Reporting Practices. JAMA Pediatr. 2015;169(1):56-62.