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CDC Methodology: Explaining The Rise In Autism Spectrum Disorder Prevalence.

Posted on | November 13, 2015 | No Comments

Mike Magee

The results of the recent 2014 CDC survey of childhood developmental diasabilities, on first glance last week, turned more than a few heads. The dramatic, but simplistic take-away was that lifetime prevalence of autism spectrum disorder (ASD) had jumped from 1.25% based on data from 2011 to 2013, to 2.24% based on 2014 data. But most of the headlines were far more nuanced, thanks to a careful and complete interpretation of the changes by the CDC.

It turns out that the methodology of the survey instrument had been fundamentally changed in order to bring the CDC survey and its’ wording more in line with other similar surveys by other branches of government including HHS and HRSA.

Screen Shot 2015-11-13 at 11.03.01 AMsource

As the illustration above shows, the earlier study included autism spectrum disorder in a group of ten alternatives in a third level of questioning. In the more recent study, Autism spectrum disorder was isolated and featured on the second level of questioning. An elaborate analysis of the complete databases of both surveys led statisticians to the conclusion, “ The revised question ordering and new approach to asking about developmental disabilities in the 2014 NHIS likely affected the prevalence estimates of these conditions.”

The new estimate of 2.24% is now in line with other estimates in governmental surveys. In addition, the CDC will be using the 2014 methodology in future studies as a benchmark for assessing any future changes in incidence. The extreme interest in trend lines for ASD reflects the fact that the cause of this strange and tragic condition remains unknown.

What is known is the following:

1. The condition is diagnosed more often in boys than girls, but that is changing. The earlier study labeled 82% as male, while the 2014 study identified only 75% male.

2. Most of those diagnosed are white (60%). 13% are black and 16% hispanic.

3. Most of the kids come from two parent families (68%).

4. The wealthy are at least as likely to have a child with ASD as poor parents. 22% are below the poverty level; 25% at one to two times the poverty level; 32% at two to four times the poverty level; and 21% more than four times the poverty level.

5. Most of the kids come from well-educated households. Over 2/3 of the parents have at least one parent with more than a high school education.
6. Geographic distribution is relatively balanced: South, 31%; Midwest, 26%; West, 22%; Northeast, 21%.

7. Most experts believe that a combination of genetic and/or environmental factors before, during and immediately after birth will eventually be found to be responsible for ASD. Vaccines as causal have been repeatedly ruled out.

 

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