A recent article on Disability Scoop discussed an upcoming CDC autism report. The MMWR’s(Morbidity and Mortality Weekly Reports) from the CDC have been one of the standards for autism prevalence for years. Each CDC prevalence estimate is calculated for a group of 8 year olds born in a certain year. For example, the last estimate was “Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, United States, 2006” for children born in 1998.
Every time a new CDC autism MMWR has come out, the prevalence estimates are higher. Every timer there are groups that point to the rising number of vaccines and mercury exposure from those vaccines. People point out that there is a correlation between mercury exposure (thimerosal) and the autism rates. The MMWR’s so far have been all for children born in the 1990′s, a period when the number of vaccines and the thimerosal exposure from those vaccines was increasing.
Here are the autism prevalence estimates from recent CDC reports:
Following this trend, the next report will be for children born in 2000, age 8 in 2008. From the perspective of testing the vaccine hypothesis, in particular the mercury/thimerosal hypothesis, this is the start of a new era. In 1999 the AAP recommended that thimerosal be removed from vaccines. By 2001, all infant vaccines with the exception of influenza were produced only in thimerosal-free versions. This means that children born in 2000, the cohort the CDC will likely report upon, received, on average, a lower exposure to thimersal than the previous groups.
If the mercury hypothesis were correct (and there already a great deal of evidence to say that it is *not* correct) the autism rate should go down. At the very least, it should stay the same as the group before–about 0.9%.
Of course we will hear claims like “but not all the thimerosal containing vaccines were gone for this group” and “but what about the influenza vaccine?” and more obvious excuses in case (at it seems likely) the prevalence goes up again.
All of these avoid the fact that the average thimerosal exposure will be much lower for this group than the previous (1998 birth year) group. The excuses amount to…well…how about a visual?
With thanks to Reuters for the image I am using.
Yes, goal posts will move. Nice idea putting them on wheels. Could save a lot of effort, but those promoting the mercury idea are already used to moving goalposts.
And what if the CDC also reports on birth year 2002 (they have reported two birth cohorts at the same time in the past)? Those goalposts might to have to move quite a bit.
Now consider a different perspective. Consider that each CDC report has been an undercount. They don’t do a “whole population” survey like was done in Korea recently. They don’t test all children, they rely upon records already in existance. The last CDC report found that about 23% of the children identified as autistic in the study did not have a diagnosis before the study. Clearly the United States has not been identifying all the autistics in the population. Given this, the rising autism prevalence estimates (and, yes, they are *estimates*) could be seen as an accomplishment. This is a position put forth by Prof. Richard Grinker. The rising prevalence estimates reflect a the U.S. getting better at identifying the autistic students in our schools.