Doping: probability that testing doesn't tell us anything new

Sir

In his Commentary 'The science of doping' (Nature 454, 692–693; 2008), Donald Berry discusses Bayes' rule, noting that consideration of P, the prior probability of guilt, is essential in interpreting a positive doping result. He fails, however, to mention what the actual value of P might be in Floyd Landis's case, which I think misses an opportunity to address an important problem.

Athlete acquaintances and the news media have led me to believe that P can be very high, and in fact approach unity, in some sports. If this is true, then anti-doping measures should cease — and not because of the statistical arguments that Berry raises, rather because the testing isn't telling us anything we don't already know.

If P is close to 1, then negative tests are most likely to be false negatives. Those who test positive might only be those who are least adept at hiding their drug use.

See also: Doping: a paradigm shift has taken place in testing Doping: ignorance of basic statistics is all too common Doping: similar problems arise in medical clinics