When I first started reading autism blogs, I was very impressed by many of the writers on what has become the Autism Hub. Amongst them, Joseph of the Natural Variation – Autism Blog.
There are a lot of armchair epidemiologists in the autism world. Joseph has always impressed me with his careful and thorough approach.
One blog post of his is where I got the title for this post: Moving Toward a New Consensus Prevalence of 1% or Higher. That post impressed me then. It impresses me even more now.
Take a look at that blog post. It is from February of 2007. Here’s a line from his intro:
The current consensus prevalence of ASD is roughly 1 in 166 or 60 in 10,000, as widely known. I believe this is still an underestimate.
Here’s a later paragraph:
Nevertheless, it appears that when ASD is screened thoroughly in a population, or when there’s a lot of awareness and good ascertainment, prevalence is found to be closer to 1%. This is not new. The following is what Lorna Wing and David Potter said on the subject as early as 1999.
Why bring it up now? Because Joseph is (once again) proven correct. The “new” consensus is about 1% or more.
The National Survey of Children’s Health shows about 1% of children aged 2-17 currently have an Autism or Asperger Syndrome diagnosis. The rumor mill has it that the CDC will release a report with about 1% soon as well.
Anyone surprised? At the least, is anyone surprised that the “official” numbers may be going up? It has been long recognized and discussed that the “official” CDC numbers are an under estimate. The regional variations alone show that to be the case (with the autism “rate” varying by about a factor of 3 between Alabama and New Jersey).
Again, lifting liberally from Joseph’s blog post: he quotes Lorna Wing and David Potter from…1999. Yep. 10 years ago.
Because we concentrated on the children with learning disabilities (IQ under 70) we saw very few with the pattern described by Asperger. We had to wait for the study by Christopher Gillberg in Gothenberg to find out how many children with IQ of 70 and above were also in the autistic spectrum. As described above, combining the results of these two studies gave an overall prevalence rate for the whole autistic spectrum, including those with the most subtle manifestations, of 91 per 10,000 – nearly 1% of the general population.
Kadesjö et al (1999) report a study in Karlstad, a Swedish town. Although this was small scale it was very intensive (over 50% of the 7 year old children seen and assessed personally by the first author). The study found a prevalence for all autistic spectrum disorders for all levels of IQ, of 1.21%!!! Children were followed up four years later and had the diagnoses confirmed.
Joseph also listed the following studies in his post:
Pervasive Developmental Disorders in Montreal, Quebec, Canada: Prevalence and Links With Immunizations by E. Fombonne, et al.. This 2006 study showed 1.076%.
More recently, we have the study by Simon Baron-Cohen’s group that showed a prevalence about 1.5%
At the time that I started reading autism blogs there was a recurring theme. Every three months the California Department of Developmental Services would publish their latest data. Rick Rollens would put out comments for the press and David Kirby would blog it, both concluding that the data showed evidence of an “epidemic”. As I recall, one quarter there were simultaneous claims of “See the autism rate went up, there’s an epidemic” and “see the autism rate went down, there’s an epidemic”. Every quarter, bloggers like Jospeh, D’oC and Prometheus (and others) would debunk the claims of epidemic.
Little has changed except that the CDDS isn’t publishing quarterly reports. Now we have more infrequent reports on autism prevalence, so we have to do the debunking less often.
The real question here is whether the prevalence of autism is really increasing. It is a very good question. It just isn’t one that we can answer with the data we have. That won’t stop people from claiming they have proof of an “epidemic”.