"Death by proxy": ethics and classification in epidemiology

Epidemiology is reductionist in that it usually relies on creating categories of people or risk factors. Classification must be undertaken as part of any study, however by the act of choosing groups, individuals are (potentially) consigned to either a higher or lower risk group. We discuss this from an ethical perspective and consider: (a) whether the groupings commonly chosen genuinely represent the risk factor of interest, (b) the implications for individuals when consigned to groups and (c) the implications for epidemiology.