RESUMO
OBJECTIVE: To differentiate between treatments in a randomized controlled trial (RCT), therapies need to display not only high purity but also high specificity. The aim of this study was to demonstrate the benefits of calculating a treatment specificity index for the evaluation of treatment differentiation. METHOD: Based on an RCT of relapse prevention in depression, comparing a cognitive with a psychoeducational treatment, the specificity and the purity index were calculated. RESULTS: As indicated by the specificity index, both conditions differed in their levels of implemented specific and common interventions. A significant relationship was found between symptom change before a therapy session and treatment specificity. CONCLUSIONS: The specificity index is an appropriate method for enhancing the internal validity of RCTs in evaluating treatment integrity.