Outline of the problem of indices of therapeutic efficacy. Components of the problem

Efficacy indices measure the efficacy of therapies. They derive, by definit ion, from two quantities, the basal or control risk of event, Re, observed in the control group, and the on-treatment risk, Rt, observed in the treate d group. In clinical trials and meta-analyses, each is an unbiased measure of efficacy. Although they are a combination of frequencies, these indices are used in clinical practice to predict the benefit in treated patients. T heir relevance to express efficacy depends on the type of clinical conditio n, and is better for acute diseases than for chronic diseases. In order to be useful for prescribers, they should meet certain specifications. In addi tion, they should be considered in the more general framework of effect mod els.