Efficacy and effectiveness approaches in behavioral treatment trials.

The objective is to clarify the distinction between efficacy and effectiveness approaches and to discuss how these approaches can be used in a complementary way in the development, evaluation, and implementation of behavioral treatments for primary headache in various settings. Efficacy studies, with an emphasis on internal validity, are experiments that evaluate treatment response in an ideal, highly controlled research environment. Despite their methodological strengths, efficacy studies are limited in their ability to estimate the treatment effects that can be expected in clinical practice settings. Effectiveness studies, with an emphasis on external validity, are outcome studies with less controls that evaluate treatment response in settings more representative of clinical practice. Effectiveness studies, however, are limited in their ability to determine the causal link between treatment and response. Based on the four-phase model used in new drug development, a three-phase linear progression model is presented for behavioral treatment studies. This model provides for pilot testing, efficacy testing, and effectiveness testing of behavioral treatments so that there is appropriate evaluation from initial promise of a developing treatment to implementation and dissemination to various treatment delivery settings.