OK, this one has been beaten to death. I am amazed that it still think that there is evidence of an “epidemic”. This is especially true of those who rely on the California Department of Developmental Services (CDDS) data. These data are so muddy as to be able to hide a real increase or a real decline.
These data have severe limitations as noted before on this blog. They are not “epidemiological” data. They are not a census of those with autism in California. They are a count of who is getting services and this can and does vary dramatically over time and geography.
That said, let’s take a look at how service rates change with time for a given birth cohort. (click to enlarge). [edit: this is the 1984 cohort] This is much as you would expect. Kids start being listed at age 3. The number increases year after year until a plateau is reached. This happens at about age 7 or 8. There is some slope to the curve: additional kids are being added to the roll even after 8 years old.
This is very straitforward and expected. But, what happens over a longer time to this cohort? Click to enlarge this graph. Ignoring the obviously leading arrow and label for now, it is abundantly clear that something unexpected has happened. A second large increase in the number of clients is observed. Why would this happen? Well, one of the possible explanations is shown by the arrow. In 1997, the “epidemic” was declared. Autism awareness increased dramatically. One possibility is that the 1984 cohort was still in school where people might notice them and identifiy them. This cohort nearly doubled in numbers from 1997 to 2003.
This brings up so many questions, many of which we just can’t answer with the data we have access to.
It would be interesting to see if there was substitution. Were these kids (heck, teenagers) listed by CDDS under a different label?
How did roughly half the kids in this cohort avoid detection? I think the new phrase is “it’s like missing a forrest fire”. Well, these forrest fires were blazing for 13 years before people started noticing them.
Also, what happened to other cohorts? Well, for one thing, a similar jump in cohort size around 1997 is observed for birth years in the 1980′s and early 1990′s. It isn’t as clear or as consistent birthyear-to-birthyear as you go back in birthyears, but it is observable in some birth cohorts. One example where one can see this is the 1960 birth cohort, which increased about 15% around year 2000.
That last paragrah wasn’t clearly written, I admit. But if you are thinking, “what? The CDDS ‘found’ 15% more 40 year olds?” you read it right. This graph (click to enlarge) shows the number of CDDS autism clients as listed in 1986 and 2007 by birth year. The 1986 (in black) data are the same as shown before. The drop in the client count in the early 1980′s is an artifact: those kids weren’t identified yet in 1986. The 2007 client count (in red) show something very interesting, at least to me.
There is an increase in autism clients for almost all the birth year groups. 40-year olds, 50 year-0lds, even older people were added to the client list as “autistic”. Again, we don’t know if or how these people were classified before the “epidemic”. They could have been (and likely were, in my opinion) clients listed in another category in 1986.
Let’s take a look at the difference between these two curves. I included data for people with birthdays in the early 1980′s, but these are not reliable. Those people weren’t through the first round of identification by 1986.
The graph shows the difference as a percentage increase. This allows us to see the older cohorts easier. At the same time, it allows people to accuse me of doctoring the data to make it seem like a bigger effect than it really is. That would be an obvious way to try to divert attention from the fact that the “epidemic” caused a roughly 40% increase in CDDS autism clients born in the 1960′s. For those clients born from 1940-1955, the increase was 70+/-28%.
Think about that a second. Autism amongst forty year old people increased by 70% during “the epidemic” years.
How can this be? How could CDDS have missed people with autism for forty or fifty years? Sure, some of these people may have moved into the state. Some of them may have been cared for by family and not been served by CDDS. The trends of these birth cohorts with time do not show the sharp rise in the late 1990′s as observed above for 1980′s cohorts. For me, this is suggestive that the those who could be identified in the school systems, were.
Obviously there are a lot of open questions here. How and why these increases were observed is a big question. Why no one has seen fit to mention this before is another question. The CDDS did not create these data sets for me. Someone else has been paying for that for some time, according to Mr. Kirby…who also hasn’t mentioned this.
People keep saying, “you can’t have a genetic epidemic”. Well, you can’t have an epidemic of a childhood onset “disease” in forty-year-olds either.
First, note that the birth cohort in the first figue above is from 1984. That is not clear. Second, here is a graph with multiple cohorts. Note that all the cohorts have an upswing in the client-numbers in the late 1990′s. Even the 1990 cohort does this. It does not appear to be based on age, but on calendar year.