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.