One of the great "myths" of the mercury militia, that movement that insists no matter what the actual scientific evidence shows that it absolutely, positively has to be mercury from vaccines that cause autism is the Myth of the Poor Excretor. In other words, the claim is that autistic children are somehow "poor excretors" of mercury, thus making the mercury that used to be in vaccines more toxic to them so that it gave them autism. One of the key pieces of evidence cited to counter this myth is a study by Ip et al (2004) that failed to find any correlation between hair and blood mercury levels and autism. This dataset was "reanalyzed" by DeSoto and Hitlan last year, sparking David Kirby to gloat that the data had been analyzed all wrong and that it really was the mercury after all!
DeSoto and Hitland were roundly criticized on a number of blogs including Photon in the Darkness and Autism Street. Dr. DeSoto responded with a long and petulant FAQ, resulting in more criticism (1, 2, 3). It was a blogospheric food fight, and Dr. Desoto ended up looking like one of the extras in Animal House.
Now, however, in perhaps the most definitive critique of DeSoto and Hitlan's "reanalysis" of the Ip et al dataset, EpiWonk weighs in. Her advice to Hitlan and DeSoto: They should actually look at the data before deciding upon what analyses to apply. She also points out in a polite way that I will turn blunt that DeSoto and Hitlan were not exactly clear in the paper about what analysis they used, leaving EpiWonk no choice but to infer it.
Best line:
I'm not making any assumptions about what DeSoto & Hitlan did or did not do in exploratory or preliminary analyses. But all I have to work with is what's in the published paper. The paper is four pages long, yet only one 8-line paragraph is devoted to the main result. On the other hand, three relatively long paragaphs are devoted to lecturing Ip and colleagues on why they (Ip et al.) should have used a one-tailed test.
And:
We can conclude absolutely nothing about the association of ethylmercury in vaccines to autism from these data.
Too bad EpiWonk didn't write:
"But we can conclude that DeSoto & Hitlan don't know beans about statistics."
I cannot believe this post has been up for this long without the militia finding it.
I think Epiwonk missed a point in her conclusion: I don't recall any info in the original study or DeSoto and Hitlan "reanalysis" as to the "source" of the Blood Mercury.
Was it all ethylmercury? (Epiwonk notes that seafood is a primary part of the diet, and mercury -- not ethyl or methyl -- is frequently found is relatively high concentrations in seafood). And, even if "yes", where did the ethylmercury come from? I see no reason to assume that children in Hong Kong receive the same types of vaccinations as those in the US (or Canada or Europe) or that the same of comparable levels of ethylmercury are used in vaccines in Hong Kong, or that the same or similar vaccine schedule is followed. Also, given the rate at which ethylmercury is excreted (as compared methylmercury), I'd think that source/date of exposure information is essential to the conclusion of DeSoto and Hitlan. Ethylmercury is excreted in days, whereas Ip used children with confirmed ASD diagnoses for comparison with her controls. I finally see no reason to assume that mercury (of whatever type) that is ingested will have the same affect as mercuty (of whatever type) injected.
I have to say that EpiWonk explains things very well while keeping it interesting. Nice reading.
one point made by the experts in the omnibus autism hearings is that it doesn't matter whether the person gets mercury in them from ethyl mercury (from vaccines) or methyl mercury (the much larger daily exposure, from food, not just fish) because once the mercury is in the brain it's in the form of inorganic mercury. DeSoto & Hitlan seemed to have been fishing for something. Funding from autism organizations or a career as expert witnesses perhaps. But their findings, as cooked up as they were, even if true didn't show inorganic mercury in the brain causes autism. Because it there is no evidence that inorganic mercury is linked to autism.
Orac,
I write to you for advice. My mother is going off the deep end; I know I don't have autism, but my mother thinks I do, and I'm afraid she may attempt to use some woo on me. As a college student who is majoring in science and planning to get a PhD, I know woo doesn't work. How do I keep her from using woo on me? Is calling the police a good idea if she tries to force it on me?
Orac,
Thanks for this post.
wfjag,
I pretty much agree with everything you say.
Orac,
I write to you for advice. My mother is going off the deep end; I know I don't have autism - my therapist knows I don't as well! - but my mother thinks I do, and I'm afraid she may attempt to use some woo on me. As a college student who is majoring in science and planning to get a PhD, I know woo doesn't work. How do I keep her from using woo on me? Is calling the police a good idea if she tries to force it on me?
Ah, crap, my computer's being stupid .
... and Kevin Bacon was in Animal House. EpiWonk to Bacon in two steps.
Sadly I don't think that KB has ever written a scientific paper so we can't do it the proper way.
Not that it is of any real importance but EpiWonk is most likely male from the post about preparing for vaccination. We should try not to hold his gender against him.
He does mention a wife. So I assume he's male as well.
Dear Epiwonk:
Thank you for the kind comment. I've had 4 stat courses (1 undergrad & 3 grad). In all of them the Profs said in the first class: "Before you decide which analyses are proper -- GRAPH THE DATA!" Your graphs were exceptionally helpful. The ASD and control children's data show at least tri-modal distributions with a very heavy skew. Analysis using arthematic means or an analysis that assumes some sort of bell curve is completely useless, and likely misleading. Your analysis was great.
Dear Anonymous:
I assume that you are an adult not under a guardianship -- and so have the legal power to make your own decisions. Making decisions on treatment is yours, not your mother's. The label for people who are smarter than the rest of us is "brillant", not ASD. If you're a "geek" and somewhat socially awkward, read How To Win Friends and Influence People and similar books (assuming that you feel a desire to be less so. I do recommend studying and practicing social skills and manners, since it makes life easier. You'll have to deal with a lot of people who aren't as smart as you over the years. Learning to make them comfortable and like you results in them being willing to listen to you and learn why what you know is important to them). Your mother fails to understand that a DSM diagnostic label will follow you throughout life. It will close doors. Although most of us are at least intimidated somewhat by truly brillant people, or are somewhat envious, the rest of us know that brillant people make the discoveries that make our lives better and longer. Best wishes for a long and successful career.
There's an update on this at EpiWonk's blog for anyone interested.