Monday, September 04, 2006

More About Mark Blaxill

In a presentation to the IOM (July 16, 2001), Mark Blaxill showed the following graph of cumulative mercury exposure (thimerosal dose per child) and the administrative prevalence of autism by birth year cohort:



Blaxill's graph was also shown in Figure 1 of Stehr-Green et al. (2003). Stehr-Green et al. conclude that there is no consistent relationship between thimerosal and autism, however. The graph also has some similarities to Figure 2 of Geier & Geier (2004) which I already critiqued. The drop in prevalence and thimerosal exposure starts one year earlier in the Geiers' paper.

The thimerosal dose per child in the graph is probably correct. The main problem with the graph is that it shows a prevalence drop in the 1995 birth year cohort. This drop is likely due to left-censorship. In other words, children in recent birth-year cohorts are too young to be diagnosed. Graphs by birth year cohort are not fixed. They change as they are revised from one year to the next. The prevalence of autism did not really drop for people born in 1995 and 1996. So the correlation shown there is either a coincidence or you would have to wait for the right year to make the graph.

In fact, a 2005 SafeMinds document by Redwood and Blaxill has a graph (second one down) which clearly shows the prevalence by birth year cohort did not drop in 1995, 1996 or 1997.

The graph from Blaxill's 2001 presentation says children were surveyed 2 years after their birth year. But this simply cannot be right. If you look at the 2005 SafeMinds document, it is clear that prevalence in a birth year cohort stabilizes at about age 8 and it's about half its peak at age 3. The 2001 graph is close to the 2005 graph, except for the 1995 birth year prevalence. The 2001 graph appears to simply show prevalence by birth year cohort, as surveyed around the year 2000.

Another problem with the graph is that it doesn't show thimerosal exposure before 1989. If it did, it would likely show a flat bar graph before that year, concurrent with an increasing autism prevalence trend. In other words, graphing thimerosal dose per child before 1989 would tend not to support the desired correlation. Geier & Geier (2004) avoids that problem by simply skipping the 1986-1989 range altogether in their graph.

Methodological problems aside, Mark Blaxill is known as a reasonable and knowledgeable individual. He clearly knows about thimerosal dosage and about autism prevalence. He must realize that birth cohorts after 2000 could not have received more than 25 micrograms of thimerosal – less than 1/3rd of what he shows for 1989. He must also realize autism prevalence is not dropping in the youngest age cohorts data is available for. As Mark Blaxill is respected by proponents of the thimerosal hypothesis, isn't he the most indicated person to put this hypothesis to rest? I think history is calling upon Mark Blaxill to do the right thing. Why is he so quiet about this nowadays?

8 comments:

  1. His good friend Lyn has a lawsuit pending, doesn't she? I can't see Blaxill standing up like a man and admitting he was dead wrong, that he's been manipulating the numbers to fit his hypothesis, probably not ever, but at least not until Lyndelle and Tommy have their day in court, or in Hollywood, as the case may be.

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  2. A whole bunch of silly people could fall if Blaxill were to step out into the light now. Wasn't he part author of a certain hair study that is cited by many many people who believe it is the mercury. I think the Geiers alone have half a dozen citations of that study, and there are many more in addition to them. To suggest that he was incorrect would probably irritate a whole bunch of "colleagues".

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  3. Trust me, Blaxill's still the same true believer he's always been. He's been knowingly manipulating statistics for years, why would he stop now?

    The problem, Joseph, is that you want to pretend these clowns are scientists and are interested in the truth. That is patently false. They're interested in their agenda, paydays, but most importantly in being right to validate the years of "self-sacrifice" they've made on behalf of the cause.

    They clearly don't want to be on the wrong side of history.

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  4. Thay may be right. And when I give people the benefit of the doubt, I don't kid myself. It's entirely possible Blaxill doesn't give a damn about scientific integrity. But let's remember he didn't get into this thing to make a buck or because he's a true anti-vax believer. He's a parent. He needs to realize that continuing to pursue unplausible causations hypotheses is unhelpful to the autism community.

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  5. Hi Joseph, I would like to answer your question about mark blaxill's silence, or at least what i think is the answer. The reason he is not quiet or trying to put the thimerosal hypothesis to rest is because, based on my correspondence with him, he needs very much to believe in it. From his point of view if he can prove that mercury poisoning caused his daughter's autism then legitimate treatments can be provided. If the thimerosal hypothesis is not pursued all potential for his daughter will be lost and he basically stated to me that arguments against an autism epidemic were doing great harm to his daughter as it would be a barrier to progress in understanding the etiology and treatments for autism. This is the great appeal of the thimerosal hypothesis to so many parents. It provides hope of a quick fix.

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  6. My message to Mark Blaxill would be that there's more hope in political activism, acceptance, research on strengths vs. weaknesses, education that is based on that research, and other such efforts. If he still wants to pursue hope through medicalization, there are other avenues that would not be dead ends. Research on the best nutrition for autistics, for example, will go on regardless of whether there has been an epidemic or not.

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  7. The statement: "He must realize that birth cohorts after 2000 could not have received more than 25 micrograms of thimerosal", would be the central flaw in this argument. While new vaccines manufactured from then on contained much less mercury, the pre-existing stockpiles of vaccines continued to be used until they expired somewhere around 2003. A drop in autism rates would therefore probably not be clear until 2008-10

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  8. In Blaxill's presentation and in other such graphs that attempt to correlate increase with increase, there are no considerations such as existing stockpiles or a 5-7 year offset to notice an increase. If they had those, the "epidemic" of autism should've started some time in 1997-1999. You can't have it both ways.

    It is generally agreed that in California thimerosal was mostly phased out by 2001. Certainly from 1999 to 2001 there must have been a drop. It's doutful the levels are maintained constant until 2001 or 2003, and then drop suddenly. For that matter, thimerosal exposure started to drop in 1995, from Blaxill's and other graphs.

    Even if we grant it's 2003, and if we assume it's true that vaccination at around 18 months causes regression as often claimed, then an impact in the 3-5 cohort should be noticed in 2004-2005.

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