If you’ve been reading about autism online, you have almost certainly read that autism “rates” are on the rise. But what if I told you that here in California intellectual disability has been dropping for over 20 years?
For many years the mainstay of the “autism is an epidemic” idea was the California Department of Developmental Services data. The CDDS keeps track of how many Californians are getting support under a number of specific disability categories. These data are publicly available (although not as easily available in the past), which makes them an easy source of data.
It’s easy to take a cursory look at the CDDS data and think “these are official data. Look at how much autism has increased!” Or claim “the CDDS only serves “severe” autism, there’s no way they were missed in the past.” You can even find a few publications to cite to back up these observations.
About a year ago I asked CDDS for some data. I hadn’t checked in a while and I wanted to see what trends are ongoing. Coincidentally, the Autism Society of San Francisco put out a report shortly after that: Autism Rising, A Report on the Increasing Autism Rates in California. So I was not alone in asking for data. The Autism Society of San Francisco made the argument that the CDDS data are accurate and show an epidemic.
The Autism Society of San Francisco graph the data in many different ways, but the one that was closest to the way I was looking at the data was in Figure 5 (click to enlarge):
and here is the caption for Figure 5:
Births of individuals later deemed to have DDS-eligible autism have been increasing sharply every year since the early 1980s. Typically intake into the system occurs between 2 and 7 years of age. The data reflects about 200 DDS autism births per year into the 1980s, but now the system is reflecting nearly 5,000 such births per year. The drop off in cases after birth year 2008 is likely attributable to usual delay in cases entering the system, and likely does not represent an actual decrease in DDS-eligible autism cases.
You can stop there and support your argument. And that’s just what most people do. Or you can question–how can I test if this is a “real” autism increase? For example, is the autism rate the same among different races? The answer is no. Is the autism rate the same in, say, San Francisco, Los Angeles, and Kern County? The answer is no. And there are many more questions one can ask of these data and over and over, the answer is no.
Either we aren’t counting all the autistics in our state, or there is something much more complex going on than vaccine, toxins, epigenetics, or whatever the claimed causes of the rise are. And I’ve gone through many of these discussions over the years. Let’s make this simple then. If one claims that the CDDS counts everyone within each disability category accurately and that the definitions they use aren’t changing with time, why is intellectual disability (mental retardation) dropping so fast in California?
You see I also graphed intellectual disability. I got autism counts, intellectual disability counts and “unduplicated” (total, each disabled person counted once) by birth year. I also got census data by birth year. And I graphed them. And anyone claiming CDDS data show an autism epidemic needs to do the same and to explain this graph, complete with the sharp peak for birth year 1993. (click to enlarge):
Intellectual disability has dropped. Off about 40% of the peak value.
If you think your idea for the rise in autism is correct, let’s take the failed vaccine idea as an example, you need to also explain how that resulted in far fewer people with intellectual disability. Plain and simple. And none of these claimed causes of an “epidemic” can explain the drop in ID.
Why bother challenging the people claiming an autism epidemic? Because it denies the existence of undiagnosed autistic adults. We have very little effort to identify those who were missed in past generations. And the likelihood is that these people–our people–are not being supported appropriately because of their misdiagnoses. And not only are we abandoning the misdiagnosed, we are failing to learn. What worked for past generations, the adults of today? What failed? What are the appropriate supports for the various needs of autistic adults? We don’t know today. And are unlikely to know by the time my kid is an adult, especially if we aren’t even looking at autistic adult needs today.
And then there’s the whole autism causation question. People spending their time trying to correlate CDDS data–data clearly confounded by numerous social influences–are unlikely to ever find a real answer.
But, for those who want to keep trying, include all the data. Give an explanation for this and you may be on to something.