How do we find out what works for whom? Evaluating the efficacy and effectiveness of psychotherapy

Controlled randomized clinical trials of psychotherapy have traditionally been used to test the efficacy of specific forms of psychotherapy for specific problems. The value of findings from such efficacy studies for practicing psychotherapists has been questioned because these studies involve clients and therapy procedures that are radically different from those typically used in routine clinical practice. Opponents of efficacy research have proposed health service-based effectiveness research as a more valuable alternative to efficacy research. Arguments for and against rigorously controlled efficacy research on the one hand, and 'real-world' effectiveness research on the other are explored in this paper.