From lbrb - Left Brain Right Brain
By Matt Carey
November 17, 2015
Last week a study was released showing an autism “rate” in the U.S. of about 2% (an estimated prevalence of 2.24% to be exact). Luckily one of the best science journalists out there focuses a lot of her attention on autism and covered this story.
I’m writing of course about Emily Willingham and her article Increase In Autism Diagnoses Not An Increase In Autism.
The study in question is Estimated Prevalence of Autism and Other Developmental Disabilities Following Questionnaire Changes in the 2014 National Health Interview Survey. The abstract is at the bottom for those interested.
While other articles are discussing the large “increase in autism”. Or, as in this Reuters article, U.S. autism numbers soar in which we read what must be a confusing message to many:
"The results reflect a near doubling in autism rates over the past three years, but the U.S. Centers for Disease Control, which released the data last week, says the shift is largely due to a change in the way the survey was worded."
Here’s the thing. Before I saw what the study was, I actually thought that the discussion was about this study: Changes in Prevalence of Parent-reported Autism Spectrum Disorder in School-aged U.S. Children: 2007 to 2011–2012. In that study, released in 2013, a 2% autism “rate” was announced.
And that was a significant change from the previous survey data (using the National Survey of Children’s Health).
And like previous estimates based on surveys, the change is at least due in large part to a change in the way the survey was presented to parents (I’m looking for a link to the discussion of the change in survey questions that affected the 2013 estimate, but there was a shift and it had a big impact).
Thankfully much of the media, and even Autism Speaks, are pointing out how this 2% figure doesn’t represent a “real” change in autism prevalence, but is largely dependent on the study methods. Others can be counted on to shout “epidemic” and ignore some of the key reasons why this doesn’t reflect a real increase.
Number 1 reason – the autism prevalence is basically the same for kids who were 3-10 and kids who were 11-17:
A real increase would show up as a higher prevalence for younger kids.
One thing we see is a decrease in disparity for autism prevalence by race/ethnicity. African Americans have a slightly lower autism prevalence (it’s unclear whether this is statistically significant or not), and Hispanics have a decidedly lower autism prevalence (1.49% vs. 2.55% for Caucasians).
Which means we still have far to go to identify and bring services to all autistics.
And it also means that the autism prevalence estimates will continue to rise as we do identify more in under diagnosed populations.
But let’s focus on the important part of that–we still have a large under-diagnosed/under-served population and it is largely among Hispanics. We really need to be focusing more attention on remedying that situation.
Here is the abstract for the current study:
The developmental disabilities questions in the 2014 National Health Interview Survey (NHIS) were changed from previous years, including question reordering and a new approach to asking about autism spectrum disorder (ASD).
This report examines survey-based estimates of the lifetime prevalence of ASD, intellectual disability (ID), and any other developmental delay (other DD) following the inclusion of a standalone ASD question, the inclusion of specific diagnoses in the ASD question, and the ASD question preceding the other DD question, and compares them with estimates from previous years.
In NHIS, one child is randomly selected from each family to be the subject of detailed questions on health conditions, functional limitations, and health care utilization. Parents are asked if a doctor or health professional had ever told them that their child had each of a series of developmental disabilities.
Prevalence estimates of ASD, ID, and other DD for children aged 3–17 years were calculated using data collected in 2011–2014.
The estimated prevalence of ASD based on 2014 data was 2.24%, a significant increase from the estimated annualized prevalence of 1.25% based on 2011–2013 data. In contrast, the prevalence of other DD declined significantly from 4.84% based on 2011–2013 data to 3.57% based on 2014 data. The prevalence of ID did not significantly change from 2011–2013 (1.27%) to 2014 (1.10%). The prevalence of having any of the three conditions was constant across survey years.
The revised question ordering and new approach to asking about developmental disabilities in the 2014 NHIS likely affected the prevalence estimates of these conditions.
In previous years, it is likely that some parents of children diagnosed with ASD reported this developmental disability as other DD instead of, or in addition to, ASD. Following these changes, the 2014 ASD estimate was more similar to ASD prevalence estimates from other sources.