Some limitations on the external validity of psychotherapy efficacy studies and suggestions for future research

Increased emphasis on identifying empirically supported treatments (ESTs) has enhanced the scientific basis for psychotherapy practice, but uncritical acceptance of ESTs as the basis for credentialing and policy decisions risks stifling innovation and creativity in the field. There are limitations inherent in efficacy studies of psychotherapy that can constrain external validity. This article discusses several limitations on the external validity of efficacy studies, as well as other issues related to evaluating psychotherapy outcome research. These limitations and concerns include: 1) the practice of maximizing homogeneity by selecting participants diagnosed with a single Axis I disorder; 2) the practice of requiring manualized therapies for efficacy research; 3) the assumption that lasting and meaningful changes occur and can be assessed within a relatively short time frame; 4) the assumption that valid assessments of outcome can be conducted in randomized control trials studies without concern for researcher allegiance; and 5) the view that evidence of effectiveness from non-RCT design studies can be ignored. Finally, alternative research approaches for studying psychotherapy that can potentially supplement knowledge gained from efficacy studies and foster continued innovation and creativity in the field are discussed.