Autism Street

By scientific definitions, a “theory“ describes a framework of understanding that can be used to make predictions and is based upon proven hypotheses. Likewise, by modern scientific definitions, a “hypothesis“ is more along the lines of an assumption or working model that has yet to be proven.

To read about how the issue of banning Thimerosal was handled
by Governor Lingle of Hawaii, read the end of this post.

It’s still a hypothesis - Not a theory 

Many proponents of a mercury-autism hypothesis have long since claimed that mercury, especially (ethylmercury) part of the preservative (Thimerosal) component that used to be prevalent in childhood vaccines, is somehow responsible as direct causative agent or trigger (in the presence of some currently unidentified genetic susceptibility) for the majority of autism. The increase in persons known/thought to be diagnosed as autistic over the past twenty years or so is often referred to, by some, as an “epidemic”.

In fact, an apparent key piece of influence, for believers in the hypothesis, is a suggested correlation between the use of Thimerosal in vaccines and the estimated prevalence of autism (often based primarily on administrative caseload as reported by the CDDS). There’s only one teensy weensy problem with this key piece of influence - the correlation doesn’t appear to exist at all, now that routine childhood immunizations are either Thimerosal-free or contain only trace amounts (<1µg of Hg per 0.5 ml dose).

For a quite decent detailed summary of the focus on autism numbers and the relative relationship of the use of California’s DDS data about autism, read this article. Although the author inaccurately uses the term “theory” in place of “hypothesis” for a scientific context, in my opinion, and fails to describe the importance of the 3-5 year-old caseload cohort, the article is informative, well-sourced, and I thought it to be balanced and broad enough to provide quick insight to anyone who may be unfamiliar with the details covered.

What do the numbers seem to indicate?

The California Department Of Developmental Services has just issued its Quarterly Client Characteristics Report for the third quarter of 2006.

The reported caseload of autistic clients in the 3-5 year-old caseload cohort continues to increase. Where there were 6,083 such clients reported at the end of the second quarter this year, there are now 6,188 such clients reported as of the end of last month.

(Click graph for larger version)

It’s fairly clear that if any major change in observed administrative caseload of autism in California’s DDS reports were to be a result of Thimerosal’s removal from vaccines (beginning in 1999 and 2000), that such a change would be observed first in the 3-5 year-old caseload cohort. Since 5 year-olds move to the 6-9 year-old caseload cohort every year, and new cases (not reported by CDDS) enter the 3-5 year-old caseload cohort every year, the 3-5 year-old caseload cohort probably currently represents the best possible indirect view of “new diagnoses” entering the CDDS system that would be observable for possible effects of Thimerosal’s removal from childhood vaccines.

Note: this is not a perfect view, and for example, could be influenced by the number of 3-5 year-olds that move in and out of state, or otherwise enter or leave the DDS system during the quarter. Also see this important note from CDDS - Data Interpretation Considerations and Limitations

The administrative caseload of autism in the 3-5 year-old caseload cohort in the end of 2002 was right around 4,000. Presumably this represents children born before 1999 who received Thimerosal at “pre-removal from vaccines” levels. The administrative caseload of autism in the 3-5 year-old caseload cohort is now well over 6,000 and representative of some children born in only very late 2000, but the majority in 2001, 2002, and 2003. If Thimerosal was causative in an observable magnitude, its removal should result in observable decrease in the total 3-5 year-old caseload cohort, and that 6,000 should quickly become the 4,000 (adjusted for population growth) very soon.

Note: it should be an observable decrease in total caseload. Eventual decreases in the growth of administrative caseload are mathematically guaranteed and expected, regardless of the etiologies of the autisms. Decreases in growth are not the same as decreases in total caseload. Additionally, administrative caseload does not necessarily represent true prevalence. It’s possible that diagnoses and administrative caseload continue to increase due to better and earlier recognition, while true prevalence declines.

The extreme case that isn’t

As pointed out to me by a fellow blogger, if Thimerosal were truly the causative agent of autism many of the mercury moms (and dads) claim it to be, we should really see that number plummet to far less if we were to adhere to their apparent beliefs. We should see something more along the lines of numbers that reflect the period pre-1992, which for California would be in the hundreds, not thousands. Not 6,000. Not 5,000. Not 4,000 or whatever - just hundreds.

Most reasonable people will recognize this as “not likely”, however, since it’s widely known and understood that:

1) The diagnostic criteria have expanded over time (the concept of autism as a spectrum of disorders did not even gain widespread recognition or have all of its formal diagnosis instruments until the early nineties)

and

2) Diagnostic substitution as a result of better awareness and recognition since then, has probably occurred much more than the mercury zealots would ever acknowledge

What’s next?

Whether or not the previous increases in administrative caseload of autism among the 3-5 year-old caseload cohort in California correlate to the use of Thimerosal in childhood vaccines, there sure doesn’t appear to be any observable corresponding decrease to correlate with its removal - at all.

The case of claiming that mercury from Thimerosal in vaccines is responsible for most, if not all autism, seems about as valid as claiming most, if not all autism is caused by being born at 10:00pm (local time) on Tuesdays (which could create a 1:168 prevalence assuming an even distribution of births across hours and days). It is hypothetically possible, but very unlikely, and extremely unlikely that such an effect would be unable to be observed. 

I’d like to say “If I am wrong, we’ll know in about 90 days” because I could be wrong, but I think “Evidence Of Harm” author, David Kirby, may have said it better to blogger Citizen Cain

But in an e-mail, he did address the key point, and concede that “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.” 

For further reading:

Research

Three Reasons Not to Believe in an Autism Epidemic
The Contribution of Diagnostic Substitution to the Growing Administrative Prevalence of Autism in US Special Education
Pervasive Developmental Disorders in Montreal, Quebec, Canada: Prevalence and Links With Immunizations
Pervasive developmental disorders in preschool children: confirmation of high prevalence
Is there an epidemic of autism?

This Blog

Autism and the “Blindness Spectrum” - Guest Blogger
ASU Professor Jim Adams on Autism Epidemiology

Other Blogs

No Autism Epidemic: An Update
FDA Decision on Thimerosal
CDDS Data, Flu Vaccines and Likely Predictions
A Listing of Articles Which Do Not Support the Vaccine Etiology of Autism Theory
A Review of the the Use of California Department of Developmental Service’s Autism Data
Questions for David Kirby– Dataphobes Beware