New Report on Autism Rates

A new report on autism prevalence rates isn’t generating many headlines.

Why?

“There was not a statistically significant change in the prevalence of children ever diagnosed with autism spectrum disorder from 2014 to 2016.”

Zablotsky et al on Estimated Prevalence of Children With Diagnosed Developmental Disabilities in the United States, 2014–2016

While the rate seemed to increase on paper, from 2.24 to 2.76%, it was not a statistically significant change. If it had been a statistically significant change, then you could think autism rates really were increasing and the report would have made headlines beyond anti-vaccine websites.

“By trying to say that there is no significant increase, is the government hoping to reassure people that autism isn’t a significant problem? That the rising number of children with autism isn’t something that anyone has to worry about? Are they trying to avoid a panic?”

Dr. Bob Sears

As most people likely understand, the term significant is used in the report as a statistical term.

When something is found to be statistically significant, then you can be fairly confident that it wasn’t caused by chance alone.

“Significance is a statistical term that tells how sure you are that a difference or relationship exists.”

What does “statistical significance” really mean?

So by stating that “there was not a statistically significant change in the prevalence of children ever diagnosed with autism spectrum disorder,” they were not “trying to avoid a panic.” There is no conspiracy.

Unlike Dr. Bob and some others, they were simply trying to not mislead people into thinking that the change from 2.24 to 2.76% meant something that it did not.

Reports About Autism Rates

Another thing to keep in mind as you think about this report – there are multiple reports about autism prevalence rates that come out every few years.

The latest report uses National Health Interview Survey data that was collected by the National Center for Health Statistics.

Unlike the autism prevalence reports from the Autism and Developmental Disabilities Monitoring (ADDM) Network that we are used to, which reported a rate of 1 in 68 children in 2016, the NCHS reports:

  • National Health Interview Survey question about autism.
    The National Health Interview Survey question about autism.

    rely on parent reports during a telephone survey – one of the questions that they are asked is if a health professional has ever told them that their child has autism, but that diagnosis is not confirmed by looking at medical or school records

  • are prone to recall bias – parents might not accurately recall what doctors have told them in the past about their child
  • have questions that have changed over the years, for example, when PDD was added in 2014, it was thought that it might have confused some parents who didn’t know that a pervasive developmental disorder is different than a developmental disorder
  • look at lifetime prevalence

And not surprisingly, over the years, the NHIS has typically reported higher autism rates than the Autism and Developmental Disabilities Monitoring Network.

autism-rates
The NCHS autism prevalence rate reports have traditionally been higher than others.

So what does this new report on autism prevalence mean?

It means the same thing that all of the other recent reports have been saying, that autism prevalence rates seem to be unchanged.

What to Know About Autism Rates

After increasing for several years, autism rates seem to be unchanged, but that hasn’t kept anti-vaccine folks from trying to get parents to panic about changes in prevalence rates that are not statistically significant.

More on Autism Rates

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