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News

Survey switch may explain rise in new autism stats

by  /  13 November 2015
Optimal order: Parents may be more inclined to say their child has autism if asked about it before they’re asked about developmental delay.

©iStock.com/ StockPlanets

About 1 in 45 children in the U.S. have autism, according to the latest estimate from the U.S. Centers for Disease Control and Prevention (CDC). The new figure represents a 79 percent increase from the estimate for 2013. It is based on a parent survey designed to track the prevalence of developmental disorders in children aged 3 to 17 years.

But there is more to the apparent jump in autism than meets the eye.

The 2014 survey asked parents about autism and then about developmental delay — the opposite of the order used in the surveys from 2011 to 2013. The researchers experimented with switching the questions because they suspected the original sequence had skewed their results.

“We’re always reevaluating our survey to make sure we’re accurately capturing the population of interest,” says lead researcher Benjamin Zablotsky, senior service fellow with the CDC’s National Center for Health Statistics.

The 2011-2013 surveys yielded a prevalence estimate of 1 in 80. A different method for tracking prevalence, which is based on medical and education records instead of parent surveys, puts the figure closer to 1 in 68. Zablotsky and his colleagues tweaked the survey to see whether doing so would make their results better align with that “gold-standard” estimate.

“We think there were children in 2011 whose parents said ‘yes’ to the question about developmental delay because they hadn’t yet said ‘yes’ to the question about autism,” he says. As a result, in that year, prevalence rates of autism would be artificially deflated.

The new data support this theory. Although the autism rate appeared to rise 79 percent over the three-year period, the rate of developmental delay dropped 36 percent.

The combined rate of children diagnosed with autism, developmental delay and intellectual disability did not change over the three years. This unchanging statistic suggests that children who were once tagged as having developmental delay or intellectual disability are now being identified as having autism.

“I think one of the take-home messages is that it really does matter how you ask these questions,” says Zablotsky. “We do believe that the 1 in 45 estimate is accurate and reliable.”


  • Lauren

    Really interesting!

  • A similar argument was made in an Op/Ed at Forbes by Emily

    Willingham, here is my post to her article which explains why this entire premise is ridiculous.

    http://www.forbes.com/sites/emilywillingham/2015/11/13/you-wont-guess-why-u-s-autism-prevalence-is-now-1-in-45/

    This Op/Ed does not even pass a basic smell test. Emily Willingham claims that the higher incidence of autism reported in the recent survey is mostly (if not fully) due to the different ordering and wording of the questions in the current survey. The ONLY evidence offered for this claim is the fact that the survey also found that the incidence of “other developmental disorders” went down. To make your case, you must assume that the incidence of these other disorders must remain constant…the fact that it does not indicates some sort of bias was either introduced or removed by the differences in the survey.

    There is a fundamental fallacy here. First, it is completely biologically plausible that the rate of autism can go up while the rate of “other developmental disorders” might go down. In fact for some of us who already understand that autism really can be caused by vaccines, and are familiar with the numerous peer-reviewed studies which support that claim, this finding would actually be EXPECTED given recent changes in the US vaccine program. Another expected finding would be the “stabilization of disparities and a closing gap between girls and boys diagnosed with autism”, but I digress. Oh wait…that is precisely what this survey found.

    But there is a second reason we know that your claim is ridiculous. For years those who deny that autism can be caused by vaccines, and this includes Emily Willingham herself, have been claiming that the rise in incidence of vaccines was not real, but due to a “diagnostic shift” which is brought about by greater awareness and better diagnostic tools. The argument made is that autism numbers are going up precisely because the numbers in the “other” categories are going down…what used to be diagnosed as other things is now being diagnosed as autism. Emily Willingham herself has made this very same argument:

    https://spectrumnews.org/news/new-spike-in-autism-numbers-may-reflect-rise-in-awareness/

    Do you see the problem here? You cannot simultaneously argue that the rising numbers for autism are not real, but reflect a shift in diagnostic strategies reflected in the lowering numbers for other categories…while at the same time assert that this very same finding in the current survey is evidence that a change in the survey itself is the reason it found a higher incidence rate found for autism.

    Some other gems from this article:

    “Not even the most die-hard causation theorist could argue that in a single year or handful of years, something environmental, like vaccines, caused a near-doubling of autism prevalence in children ages 3 to 17 years.”

    Um, has Emily Willingham and Forbes been paying ANY attention over the past 15 years? Here is CDC data showing that the incidence of autism increased by 100% over a period of 4 years. It is also clear that the rate of increase itself is increasing. The last finding of 1-in-68 is from children born in 2002, so we would actually expect to find not only a higher incidence now, but one that reflected an increased rate of change (remember your high school calculus?):

    http://www.cdc.gov/ncbddd/autism/data.html

    “The report also shows some stabilizing of previous disparities and a closing gap between girls and boys diagnosed with autism.”

    Now WHY would that be?

    “Prevalence also is lower among uninsured families, possibly reflecting an access issue.”

    I think you are ON to something! But access to what, Emily?

  • Ethyl

    I’m kind of a guppy, but I still don’t think the CDC went door to door last year…ha!

    The one in 45 number included kids who had ~ever~ had a diagnosis of autism. It seems about one third had lost their diagnosis. It was an interesting, serendipitous question that inadvertently showed how many kids had once been labelled autistic, and for whatever reason, no longer were. Fully one third of the parents no longer identified their previously identified children as autistic.

    Correct me if I’m wrong because I’ve been blasting this all over.

    • Ethyl

      This comment seems strange because I had two open tags on my computer. I commented on the wrong one!

      “It is unclear how the new estimate stacks up against other measures of autism prevalence. Late last year, the CDC reported that 1 in 45 children have autism, based on an annual door-to-door survey.” from https://spectrumnews.org/news/u-s-stats-show-autism-rate-reaching-possible-plateau/

      We guppies do that a lot.

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