Drug-Eluting Stents: Efficacy, Effectiveness, Efficiency, and Evidence

Public health systems aim to improve the health of a population at a cost whose limits are set, one way or another, by society. To ensure that the health of a population is improved, clinical procedures that are supported by scientific evidence of a more favorable outcome (risk/benefit ratio) compared to any other alternative should be used. To ensure that the outcomes are achieved at an acceptable social cost, the cost of obtaining an outcome with each of the technically possible alternatives should be known. The outcome of a health intervention can be measured by efficacy (in ideal experimental conditions), effectiveness (in real everyday conditions), utility (survival time adjusted for quality of life) and benefit (outcomes expressed in monetary units). The best scientific evidence on the outcome of therapeutic interventions comes from randomized clinical trials with no methodological weaknesses. That is, clinical trials provide information on the efficacy of the interventions. Efficacy is necessary for effectiveness but it alone is not sufficient. Effectiveness depends not just on efficacy but also on local factors, which may differ from those of the clinical trial (technology, experience, organization, etc). Efficiency is the ratio of the outcomes to costs that have to be met to achieve the outcome, thus classic efficiency analyses evaluate cost/efficacy, cost/effectiveness, cost/utility, and cost/benefit.1 When a new technology appears in medicine, the key questions focus on the outcomes and the costs with respect to existing technologies, though the answers to these questions do not usually come quickly. Thus, some effective techniques spread slowly ED I TO R I A L S