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Yes, Autism Diagnoses Are Up – But That Doesn’t Mean The Disorder Is More Common

autism diagnosis

The Centers for Disease Control and Prevention reports that the prevalence of the autism spectrum disorder (ASD) among 8-year-olds has increased to one in 68, a 30 percent increase since the agency estimated just two years ago that one child in 88 suffered from the disorder.

The CDC’s report is based on a review of records—from psychiatrists, schools, pediatricians, physical therapists, neurologists, and psychologists—from 11 different geographic regions in the U.S. There is huge variation between those regions: one in 175 children was diagnosed with the disorder in Alabama, compared to 1 in 45 in New Jersey. There is also a huge variation in race, as white children were far more likely to be identified as on the spectrum than black or Hispanic children.

For some, these numbers probably look alarming. But don’t panic — evidence strongly suggests that, although the number of diagnoses has gone up, the disorder itself may not actually be on the rise.

As this report numbers are likely attributable to a combination of factors, including shifts in diagnostic trends and the rapidly increasing awareness of autism.

For this report, the CDC looked at kids who have been given a diagnosis on the autism spectrum but also at kids whose reported symptoms fit the criteria for ASD but have not been officially diagnosed—the idea being that the CDC would catch the kids who were falling through the cracks. But the CDC didn’t find more kids in states like Alabama and Colorado who fit the criteria but weren’t already diagnosed than it did in Maryland or Jersey, where rates of autism are higher. Since there is no rational reason to believe that kids in New Jersey just naturally have four times the rate of autism that kids in Alabama do, the numbers suggest that kids in the states with lower numbers are not being referred for a diagnosis, and/or that the experts are not giving good enough notes.

The same goes for racial disparities. The notion that there are such glaring discrepancies in diagnosis among children of different races is disturbing, and it also indicates that there are problems with the way we have been diagnosing and counting autism cases. The CDC agrees, and notes in the report’s conclusion that they are working to account for the racial and geographic discrepancies.

An increase in autism… or an increase in autism diagnosis?

That the number of new autism diagnoses is dramatically increasing is generally accepted and not a point of debate. However, a growing line of evidence suggests that a large proportion of new autism diagnoses are attributable to the dual effects of increased awareness (leading to more diagnostic capture) and widespread diagnostic reclassification (specifically, reclassification of children with intellectual disabilities as being autistic, instead), rather than a true increase in the prevalence of autism.

In the 1990’s the diagnosis of autism was changed to autism spectrum disorder (ASD) – the new name reflecting the changing concept of autism to include a broader spectrum of symptoms, including much more subtle manifestations. In particular a diagnostic entity known as Aspergers syndrome, which is essentially a subtle manifestation of autism features, was classified as part of ASD. Any time you broaden a category the number of individuals that fit into that category is likely to increase. In Denmark, a similar change in diagnostic criteria was found to account for as much as 60 percent of the nationwide increase in prevalence of autism spectrum disorders

As autism researcher Dr. Eric Fombonne concluded in a 2005 study:

Recent epidemiological surveys of autistic disorder and other PDDs have heightened awareness of and concern about the prevalence of these disorders; however, differences in survey methodology, particularly changes in case definition and case identification over time, have made comparisons between surveys difficult to perform and interpret.

In addition to the broadening of the diagnosis, the societal acceptance of ASD has dramatically increased. There has been increased efforts at surveillance – scouring the community for hidden cases of autism. Further, parents have become much more accepting of the diagnosis, which may partly be due to the fact that is some states the label with facilitate access to special services. And clinicians have become more knowledgeable of ASD so are better able to make the diagnosis, even in subtle cases. This explains why, according to the CDC report, there are now more autism cases with milder symptoms. In 2008, 62 percent of children with ASD did not have an intellectual disability (which means an IQ over 70). In 2010, 69 percent of children did not have an intellectual disability.

Studies suggest that “diagnostic substitution” or reclassication — moving people from one diagnostic category, such as “mental retardation” or “language impairment,” to the autism category — may also play a role in the increasing numbers of autism diagnoses. For instance, in one recent study, researchers at UCLA re-examined a population of 489 children who’d been living in Utah in the 1980s. Their first results, reported in 1990, identified 108 kids in the study population who received a classification of “challenged” (what we consider today to be “intellectually disabled”) but who were not diagnosed as autistic. When the investigators went back and applied today’s autism diagnostic criteria to the same 108 children, they found that 64 of them would have received an autism diagnosis today, along with their diagnosis of intellectual disability.

Further evidence of this shift comes from developmental neuropsychologist Dorothy Bishop and colleagues, who conducted a study involving the re-evaluation of adults who’d been identified in childhood as having a developmental language disorder rather than autism. Using two diagnostic tools to evaluate them today, Bishops’ group found that a fifth of these adults met the criteria for an autism spectrum diagnosis when they previously had not been recognized as autistic.

The most recent and compelling evidence comes from a Penn State study that found that almost all of the increase in U.S. autism diagnoses over the first decade of this century was the result of reclassification. According to a Penn State press release, the study “found that the increase in students diagnosed with autism was offset by a nearly equal decrease in students diagnosed with other intellectual disabilities that often co-occur with autism. The researchers conclude that the large increase in the prevalence of autism is likely the result of shifting patterns of diagnosis that are complicated by the variability of autism and its overlap with other related disorders.”

Though this evidence in itself doesn’t mean that the prevalence of autism has not increased at all, it does say very emphatically that the huge uptick in the numbers of children diagnosed with autism likely has much more to do with how we diagnose the condition than how common it actually is.



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