I should start this new post by explaining why I’ve been mostly absent for the last month. September was an interesting and challenging month. I could say it was a perfect storm, combining the start of the academic year, preparing a new graduate seminar I had never taught before, transitioning into my new role as Assistant Professor at the University of Michigan, and rushing to get my new research laboratory functioning. Fortunately however, things are finally settling down and I can start to catch up with the child psych literature. I hope from now on I will be able to write a new post every Monday morning.
I thought it would be appropriate to start the month with some thoughts about the new Autism prevalence study that was just published in Pediatrics and which hit the news cycle this morning.
In sum, the study found that the prevalence of parent-reported rates of autism was higher than previous estimates. Specifically, they found that 1.1% of all children aged 3 to 17 had autism (1 in 91) as compared to previous estimates of approximately 1 in 150.
Does this suggest an increase in autism rates between 2003 and 2007? Maybe, in that the finding is consistent with the possibility that autism rates are increasing. However, there are a number of issues that must be taken into account, especially the methodological differences between this study and the CDC study that reported prevalence rates for 2002.
For a more detailed explanation of the CDC report from where the 1 in 150 rate comes from read my previous post on the topic: Autism rates in the USA: where did the 1 in 150 number came from?
How was the current study conducted?
The study include an analysis of the 2007 National Survey of Children’s Health (NSCH). The NSCH consists of a random and representative telephone survey of parents of 78,037 children. Each family provided data on a single child, so that if a family had more than one child, only one of the children was selected as the target child for interview purposes. During the interview the parents were asked whether “they had ever been told by a doctor or other health care provider that their child had ‘autism, Asperger’s disorder, pervasive developmental disorder, or other autism spectrum disorder.’ “ If the parent said yes, then they were asked whether the child currently had autism or another ASD.
They found a prevalence of 110 cases of current ASDs per 10,000 children, or 1 in 91 children. As expected rates were 4 times higher in boys than in girls.
There are two key differences between this study and the previous CDC report:
- Unlike the CDC report, this study was nation-wide and included all US regions. In contrast, the CDC report was based on autism rates observed in only 15 states. Therefore, the current report appears to be more representative of the US population than the previous study.
- The current study was based on parental reports during a phone survey with no corroboration of the diagnoses endorsed by the parents. That is, we assume that parents are correct when asked… does your child current have Autism or ASD? The authors could not verify the veracity of these parental reports through review of medical or educational records. In contrast, the CDC report was based on a review of medical and educational records, and documented diagnoses were doubled checked by trained clinicians to make sure that there was sufficient evidence for each diagnosis. Therefore, the CDC study was much more conservative in estimating autism rates because diagnoses were obtained from medical and educational records rather than from parental reports.
Clearly, neither the CDC nor the current Pediatric study is near perfect, and they provide only a rough estimation of autism cases in the US. Unfortunately, the very significant differences in methodology between these two studies make it impossible to determine with certainty whether the new rate of 1 in 91 reflects a true increase in autism or is simply a byproduct of different estimation procedures not used in previous studies.
The reference: Michael D. Kogan, PhD,a Stephen J. Blumberg,, PhD,b Laura A. Schieve, PhD,c Coleen A. Boyle, PhD,c, James M. Perrin, MD,, Reem M. Ghandour, DrPH,, Gopal K. Singh, PhD,, Bonnie B. Strickland, PhD,, Edwin Trevathan, MD, MPH,, & Peter C. van Dyck, MD, MPH (2009). Prevalence of Parent-Reported Diagnosis of Autism Spectrum Disorder Among Children in the US, 2007 Pediatrics, 124 (4) : 10.1542/peds.2009-1522
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