Is there an evidence-based number of sessions in outpatient psychotherapy? – A comparison of naturalistic conditions across countries

Deciding on the number of psychotherapy sessions to satisfactorily treat a patient is a vital clinical as well as economic issue in most mental health systems worldwide. The length of outpatient psychotherapy in naturalistic conditions ranges from a single session to hundreds of sessions [1]. In randomized clinical trials, the number of sessions is typically fixed to deliver manualized treatments and to control for dosage effects (e.g., in a 16-session format [2]). Using data from Routine Outcome Monitoring studies [3, 4], we investigated whether the treatments under naturalistic conditions were fixed to a particular number of sessions or not (H1), whether naturalistic conditions tended to include unusually long treatments (e.g., >100 sessions) (H2), and how the observed number of sessions was distributed across countries (H3).