Efficacy and effectiveness: The wrong use of different terms

      In the last century the use of two terms were agreed, efficacy and effectiveness, to name two different types of assessment [
      • Institute of Medicine
      Assessing medical technologies.
      ]. Efficacy assesses the performance of interventions used in controlled, ideal conditions; effectiveness evaluates interventions in routine care conditions [
      • Institute of Medicine
      Assessing medical technologies.
      • International Epidemiological Association
      ]. This applies to all trials, regardless the type of assessed interventions. When referring to the development of new regulated interventions (medicines, devices) all prelicensing trials (phases 1 to 3) assess efficacy: current clinical trials regulations and the design, conduct (highly controlled conditions) and nature and extent of data to be gathered to gain regulatory approval make it almost impossible to assess effectiveness. However, in post-marketing phase 4 trials, investigators could assess efficacy or effectiveness depending on their closeness to routine clinical care conditions. In this type of trial, a pragmatic approach leads to obtaining effectiveness data.


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