Monday, 20 July 2015

Epo and doping accusations in the Tour de France – the numbers never lie (or do they?)


I was struck by the vehemance of the current anti-Froome accusations. So I thought I would add my tuppence worth to this story. First let me nail my colours to the mast. I have a lot of sympathy with Sir Dave Brailsford when he says “"It is not possible to prove a negative. I can't," [1]. 
Sir Dave is referring to the well-known fallacy in formal logic known as an argumentum ad ignorantiam or “appeal to ignorance”. This poses that “something is true only because it has not been proved false, or that something is false only because it has not been proved true”.
Now there are some cases where versions of this argument are used by philosophers (inductive logic relies on it in part). Indeed you cannot prove any future event true or false until it has happened. Prehistoric man with no knowledge of physics or astronomy had no definite “proof” that the sun would rise tomorrow or that walking off a cliff would result in a fatal fall. However, enough evidence had accumulated from previous life experiences to make these perfectly reasonable assumptions. Indeed it would be impossible for us to live our lives without making these kind of inductive “leaps of faith” every day.
Something ought to go without saying given the scientific literature, but clearly it needs repeating ad infinitum. Doping allegations based purely on performance (in this case speed or power data) fall well short of the strong evidence required for inductive reasoning. Power/time data alone can never prove someone is doping, or even make it probable. If you doubt this please take time to read carefully the recent article by Hein FM Lodewijkx “The Epo Fable in Professional Cycling: Facts, Fallacies and Fabrications” [2].
Not that the Lodewijkx review does not prove that epo does not improve performance; in fact it is careful not to say this.  Times have continually improved in the Tour and doping could be one of many factors that can affect racing times. The devil is in the scientific detail. But it does make salutary reading for people who assume that numbers alone are a reason for crying foul.
One thing that is needed is a proper randomized trail in elite cyclists testing whether epo doping “works”. Crucially, it should include accounting for the likely strong placebo effect (as everyone “knows” epo works – see my previous blog). The definitive study would include giving cyclists epo when they were told they were getting placebo. This kind of approach has been very successful in studies comparing drug and placebo effects on performance following caffeine administration [3]. However, significant ethical issues would need to be overcome before any epo study could start. Worse still cyclists would need to volunteer for a “ban” so it also need an end of career altruistic act.
If such a study were performed, my suspicion is that it would show that epo microdosing is no more effective than a strong placebo. I suspect blood transfusions or high dose epo would outperform placebo, but I doubt those more severe studies could be done. Still I don’t “know” these answers – as a scientist I just want the studies to be done (ethics permitting) to find out!

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