Efficacy and effectiveness: The wrong use of different terms

Published: 2 May 2018
Author(s): Rafael Dal-Ré, Frits Rosendaal
Issue: May 2018
Section: Letter to the Editor

In the last century the use of two terms were agreed, efficacy and effectiveness, to name two different types of assessment [1]. Efficacy assesses the performance of interventions used in controlled, ideal conditions; effectiveness evaluates interventions in routine care conditions [1,2]. 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.