Friday, December 14, 2018

Why autism at 2.5% isn’t surprising.

Let’s get one thing out right away–autism prevalence studies undercount. Not all autistics are diagnosed. That’s just a fact. Consider the recent CDC study. They look at school and medical records. In many cases, they find children are autistic based on their records–but the schools and doctors hadn’t diagnosed those children.
Combining data from all 11 sites, 81% of boys had a previous ASD classification on record, compared with 75% of girls (OR = 1.4; p<0.01). 
Yeah, more than 20% of the kids counted in their prevalence had no diagnosis. They and their families didn’t know.
And, if there isn’t enough in the records to show a kid is autistic? That kid gets uncounted altogether. 
So, when people look at the CDC prevalence estimates from over the years and cry “epidemic”, well, there’s a reason why those people usually have some causation theory that they believe in. The irony is that they are usually wrong that their theory needs an epidemic to support it. But, heavily biased people are not usually the best sources of reliable analyses.
What would be a better method of counting how many autistics are in a population? Sounds obvious–test all the kids in a given population. Equally obvious–this is a much more expensive and difficult task. One such study was published in 2011. Yes, 7 years ago. In Prevalence of autism spectrum disorders in a total population sample, the autism prevalence in Korea was found to be 2.63%.  A study performed in South Carolina and reported at IMFAR last year found a prevalence of 3.62%.
This all said, we had another autism prevalence come out this week–The Prevalence of Parent-Reported Autism Spectrum Disorder Among US Children. This study found a prevalence of 2.5%.
Now here’s a nice thing about this recent study–OK, two nice things. First, they don’t just look at kids of one age. Second, you can obtain the data. Which I did. Let’s look at the autism prevalence broken down by birth year.