A therapeutic index: measuring therapeutic actions in psychotherapy

This article describes a research method that measures a therapist's effectiveness by assigning a composite value to each therapeutic verbal statement during a session. The intrasubject averaging of these values is called the mean therapeutic index (sigma). In this study, whether the mean therapeutic index could be used to predict treatment outcome was investigated. A successful case and an unsuccessful case were selected for 15 therapists, and an early session for each case was coded using the mean therapeutic index. The results show that the magnitude of the effect of the mean therapeutic index, as indicated by the correlation coefficient r, was .92 (r2 = 0.85). Thus, the mean therapeutic index accounted for 85% of the variance in the classification of treatment outcome as successful or unsuccessful. The findings point to the method's potential use for clinical practice and supervision of psychotherapy.