Efficacy and Effectiveness

Efficacy and effectiveness, while similar in meaning in every day language, have very specific meanings in the context of medical research and outcomes studies. Efficacy research is designed to investigate how well a treatment works under carefully controlled conditions (i.e. clinical trials).

Effectiveness research attempts to discover how much benefit results from use of the treatment in real world settings.

See Steiner, 2002 for for a discussion of this distinction in psychiatric research.