Randomized controlled trials (RCTs) are considered the best methodology for studying the efficacy of psychotherapy. Optimally an RCT design makes it possible to conclude that if one treatment has a better outcome than another, this is due to the treatment package (TP) as it was implemented in this particular context, rather than other factors beyond the treatment (= high internal validity). | The neglect of treatment-construct validity in psychotherapy research: A systematic review of comparative RCTs of psychotherapy for Borderline Personality Disorder
