Influence of depression severity on the relationship between interpersonal synchrony and perceived session quality during psychotherapy

Background and aims. Interpersonal synchrony between therapists and clients has been linked to positive psychotherapy outcomes and improved therapeutic alliance. However, psychological factors may influence how synchrony affects clients’ experiences during therapy sessions. This study examined the moderating role of depression severity on the relationship between client-therapist interpersonal synchrony and perceived session quality in a Pakistani clinical population. Methods. This prospective observational study included 35 adult patients receiving supportive-expressive psychotherapy for depression in outpatient mental health clinics in Karachi, Pakistan. Interpersonal synchrony between patients and therapists was assessed using the Coding Interactive Behavior System across five video-recorded therapy sessions. After each session, participants rated perceived session quality using a standardized 7-point Likert scale questionnaire. Depression severity was measured at baseline using the Patient Health Questionnaire-9. Multilevel modeling (MLM) was used to analyze the relationship between interpersonal synchrony and perceived session quality while accounting for repeated sessions nested within individuals. Results. Higher levels of interpersonal synchrony were significantly associated with greater perceived session quality across therapy sessions. Depression severity showed a significant negative association with session quality and moderated the synchrony-session quality relationship. The positive association between synchrony and perceived session quality was stronger among participants with lower depressive symptom severity and weaker among those with more severe depression. Conclusions. Interpersonal synchrony appears to play an important role in shaping therapeutic experiences, although its impact may vary according to depression severity. Therapists should consider depressive symptom burden when fostering interpersonal attunement during psychotherapy to optimize therapeutic engagement and outcomes.