Sir

In his Commentary 'The science of doping' (Nature 454, 692–693; 2008), Donald Berry claims that anti-doping tests are based on flawed statistics. Your Editorial 'A level playing field?' (Nature 454, 667; 2008) goes even further in concluding that the anti-doping authorities act unscientifically. These claims neglect an abundant body of literature and ignore the paradigm shift that has taken place in anti-doping science.

Anti-doping is a forensic science, not a medical one. In medical diagnostics, biostatisticians have all the leeway to set sensitivity and specificity to an appropriate level. Such freedom is restricted in forensics: the risk of a false positive must be minimized at every step of the development, validation and application of a test. This fact alone explains why anti-doping tests do not necessarily rely on statistical reasoning, and certainly not solely on a specificity threshold, something Berry seemingly takes for granted. For the detection of exogenous testosterone in particular, anti-doping laboratories establish intervals for a reference population throughout validation processes that also include quality controls for batch acceptance. To date, no false positive has been reported among all the negative controls.

The nature of scientific evidence is also different. In forensics, the traditional assumptions of 'absolute certainty' and 'discernible uniqueness' are being progressively abandoned in favour of an empirical and probabilistic approach (see M. J. Saks and J. J. Koehler Science 309, 892–895; 2005). In the fight against doping, this is embodied by the 'athlete's biological passport', an electronic document that stores an individual's information pertaining to indirect markers of doping.

In multiplying the probabilities to estimate the specificity for the Landis case, Berry makes a basic statistical error. Indeed, successive tests are not independent in a longitudinal follow-up (P. E. Sottas et al. Forensic Sci. Int. 174, 166–172; 2008).

A more thorough literature search would have prevented Berry from attempting to reinvent the wheel and from concluding that anti-doping scientists are “on the wrong path”, which is presumptuous and disrespectful. The role of anti-doping science (not “doping science”) is to protect clean athletes. Your Editorial may have just the opposite effect.

See also: Doping: probability that testing doesn't tell us anything new Doping: ignorance of basic statistics is all too common Doping: similar problems arise in medical clinics