Sir

Donald Berry's Commentary 'The science of doping' (Nature 454, 692–693; 2008) is like a breath of fresh air in the murky world of drug testing. Unfortunately, a lack of competence in basic statistics is all too common in biology and the clinical sciences. As Berry points out, there is often a lack of accounting for pre-test probabilities in the application of tests with known sensitivities and specificities, as well as for issues arising from multiple testing.

Even those who grasp the principles of Bayes' rule frequently make the mistake of not empirically confirming the utility of confirmatory assays. Take steroid testing, as illustrated in Berry's Figure 1 for Floyd Landis's case in 2006. Given the high sensitivity and specificity of the assay, androsterone plus 5a-androstanediol is assumed to form the basis of a conclusive set of tests for confirming positive screening results with etiocholanone plus 5b-androstanediol. In fact, the confirmatory tests can provide little additional information unless they have been shown to be independent predictors of drug positivity.

See also: Doping: a paradigm shift has taken place in testing Doping: probability that testing doesn't tell us anything new Doping: similar problems arise in medical clinics