Incidence In California Not Dropping - A RecapSince 2001 all vaccines routinely recommended in the U.S. have contained only trace amounts (< 1 µg) of thimerosal. Thimerosal hypothesis proponents naturally expected the incidence of autism to drop as a result. In the absense of detailed ongoing epidemiological studies on autism incidence, they turned to administrative data, particularly that provided by the California Department of Developmental Services (CDDS) on a quarterly basis. CDDS, however, only publishes data on population sizes (caseloads), not data that could be used to determine incidence, such as numbers of clients entering the system every quarter.
Nevertheless, thimerosal hypothesis proponents came up with the notion that substracting the caseload one quarter minus that of the previous quarter is equivalent to the number of clients entering the system. This naive understanding of population dynamics led to claims that the incidence ("rate") of autism was beginning to show modest drops in California. These claims were quickly picked up by the press, which repeated the error verbatim.
The net difference in the numbers between quarters was dubed "New Cases", implying that this is roughly the number of children diagnosed in a quarter. Unfortunately, caseload numbers in the quarterly report represent only clients with active status. As CDDS itself explains in a document titled Data Interpretation Considerations and Limitations, differences in the numbers from quarter to quarter represent the net changes between newly reported clients and drop-outs. The significance of drop-outs should not be understated. Drop-outs include clients who have died, who have moved out of the state, who have been found to no longer be eligible for services, who have decided to no longer pursue eligibility, or who have had a change in their CDER category.
In fact, there is a report titled Active Status Population: Growth Analysis by California State University, Sacramento. It documents number of "New" clients and number of those who "Leave", from 1999 to 2004 (see page 7). The report shows that the number of clients who leave the system is not insignificant and was growing as of 2004. There is a small drop of 2.7% in new clients between 2002 and 2003, but this number grows again by 3.6% in 2004. The small drop in 2003 corresponds to a California law change (CA AB1762, W&IC 4512) specifically crafted to depress autism caseload growth. (Many children likely lost their CDDS eligibility after this law passed).
A good analogy for "New Cases" is "Number of Births" defined as the difference in the population one year minus that of the previous year. If "Number of Births" is defined this way, imagine what the "Number of Births" per year might be in a country with a constant population size.
We also know that the autism caseload in California is currently growing at a rate of about 10% annually, whereas the California population grows at a rate of 1.3% or so annually. It is unlikely that autism incidence is dropping given this fast caseload growth rate.
Nevertheless, caseload growth (what thimerosal hypothesis proponents call "New Cases") must drop necessarily. Let us imagine that annual caseload growth remains at around 2,500 indefinitely. Given population growth in the state of California, autism caseload would stabilize at about 192,000 in 64 years, which is highly unlikely. It is more probable that autism caseload will stabilize in about a decade at 40,000 to 50,000 with an annual caseload growth of 520 to 650 (130 to 162 quarterly).
Another way to tell that incidence is not dropping is to look at the 3-5 cohort caseload. Numbers in this cohort should change quickly in response to incidence changes. Consider that 5 year olds in the cohort will no longer be in the cohort next year. So it is necessary for many children to enter the cohort every year to maintain the caseload. We can see in the CDDS data that annual caseload growth in this cohort is about 10%. So it is highly unlikely that incidence is dropping.
Now that we have established that the incidence of autism is almost certainly not dropping in California, and that gradual drops in caseload growth are expected and not remarkable, let's see what thimerosal hypothesis proponents have said and continue to say about this issue.
David KirbyOn August 11, 2005, Citizen Cain attempted to inform David Kirby on the difference between 'entries' and 'net gain'. The post is long already, so let's just say David Kirby finally agreed to the following:
If the total number of 3-5 year olds in the California DDS system has not declined by 2007, that would deal a severe blow to the autism-thimerosal hypothesis.
Note that Kirby accepts it should be a drop in the total number of 3-5 year olds, not a drop in the growth, or a drop in the growth of the growth, or any such nonsense. Yet, right after the Q1 2006 CDDS report came out, Kirby decided to grasp at straws and claimed in EOHarm that "yearly trends for 3-5 year olds are down" based on gradual drops in caseload growth in the 3-5 cohort. Again, he agreed there should be drops in the caseload. Drops in caseload growth are not meaningful.
And as Kevin Leitch points out, at the latest Autism One conference David Kirby apparently forgot what he told Citizen Cain. I have to wonder if this is honest forgetfulness or something Kirby feels he needs to do as the author of Evidence of Harm.
Geier & GeierEpidemiological studies generally discuss prevalence or incidence. It was thus surprising that the journal JPANDS, a purportedly peer-reviewed journal, accepted a paper by Geier & Geier where they used the flawed "New Cases" terminology instead.
After I pointed out the significance of this error to the Editor-In-Chief of JPANDS, and my comments were forwarded to the authors, Mr. David Geier requested data on "new consumers with autism" (true new cases) from CDDS, in what appeared to be a frantic move. I was excited CDDS would release this data after it was funded, because this data would settle the issue (and would've been great blogging data). Unfortunately, months passed, and CDDS could not complete the work because it was not funded. Clearly, Geier & Geier either could not make the payment (which was probably less than what they charge a single client of theirs) or they were not interested in having this data become public.
A response to a commentary in JPANDS shows that Geier & Geier had decided instead to try a new party line. They would now tacitly admit to the error but claim that the "New Cases" calculation is an acceptable approximation on the basis that drop-outs are probably not significant:
Note than once a patient officially enters into the CDDS program, he is entitled to benefits for life. This method of analysis does not adjust for potential increases or decreases in the number of persons with the diagnosis of autism owing to factors other than a new diagnosis, such as population migration or death. While such events occur, it is highly unlikely that their frequency is changing from year to year in a manner that would account for the observed trends.
Geier & Geier must not be aware of the University of California active status population report, where we can see that drop-outs are significant and do change significantly from year to year. Further, Geier & Geier fail to note changes in eligibility and diagnostic category. Of course, if they had gone ahead and funded the work they requested CDDS to do for them, we could discuss this issue with better facts at our disposal.
Rick RollensRick Rollens is perhaps the anti-thimerosal activist who has more often used the flawed "New Cases" terminology to claim that autism rates are dropping in California. To his credit, this is probably just honest ignorance. I do not believe he has strayed from this script, and has used this terminology up until the very last report from CDDS.
Wade RankinI don't know for sure what Wade Rankin thinks of the "New Cases" issue but he has said the following:
On a policy note, Rick Rollens addressed the California numbers and, more importantly, the California response to those numbers. The California DSS numbers are undeniably controversial and subject to various interpretations. But a sensible look at them indicates that something is indeed going on, and Californians should be grateful that people like Mr. Rollens are there to see that society doesn't simply bury its collective head in the sand.
For this to be about something that is "going on" in the present tense, he must be referring to claims of an incidence drop. Sensible things can usually be explained. I hope Wade can come by and explain the sensible reasoning by which we can arrive at the conclusion that "something is indeed going on" in California.