New thimerosal/autism paper – signal vs noise

13 Sep

The new thiomersal paper that Sully has blogged will be attacked by the antivaxxers in at least one key area. The area that will be attacked is – to those well schooled in the way good science operates – a standard way to improve the signal to noise ratio of the results. Or to put it another way, ensures ‘cleaner’ results.

From the paper:

…Children were excluded if they had the following medical conditions with known links to ASD traits: fragile X syndrome; tuberous sclerosis; Rett syndrome; congenital rubella syndrome; or Angelman syndrome…

So first of all why were children that fell within these groups excluded? As I said, the answer is to ensure better data. In order to get a cleaner signal, the more noise that can be eradicated the better.

In this instance, children who already have existing medical conditions known to be related to autism would produce noise. We already know what caused their autistic traits hence establishing a clear link to thiomersal would not be possible. In a very meaningful way, doing this does a large favour for antivax group. If these children were eradicated from the study and a clear link to thiomersal _had_ been established then denying the link would be very much more difficult.

However don’t expect the antivaxxers to see this. Or even if they _do_ see it, they will look away purposefully. They will use the fact that these children were excluded and say _”See? ‘They’ have to hide the autistic children!”_ .

When you see this tactic – and you will see it – see it for what it is. It’s simple noise generation to obscure the clear signal coming through. Thimerosal in vaccines doesn’t cause autism. And it never did.

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2 Responses to “New thimerosal/autism paper – signal vs noise”

  1. Leila September 13, 2010 at 17:31 #

    A better way to explain this is that they excluded those medical conditions because they are clearly not caused by vaccines, they have identified genetic/congenital causes for it.

  2. Joseph September 13, 2010 at 21:57 #

    By analogy, suppose you wanted to determine if french fries cause lung cancer. If half your sample are smokers, you’ll have a lot of noise. Many of your positives will probably be smokers. They are not informative in relation to what you’re looking for. Plus there are other problems. Perhaps smokers tend to eat french fries. You’re much better off excluding smokers altogether.

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