Dynamic expectancies: The independent role of within-person change in outcome expectancy in predicting overall treatment outcomes in psychotherapy for depression

Objective: Dynamic changes in patients’ outcome expectancy have been increasingly recognized as important for psychotherapy success. However, whether expectancy change predicts treatment outcomes independently of baseline expectancy, particularly in major depressive disorder (MDD), remains underexplored. This study investigated the role of expectancy change throughout treatment as an independent predictor of psychotherapy outcomes in MDD. Methods: Seventy-five patients with MDD underwent a 16-session psychotherapy treatment, during which expectancy was measured six times. Expectancy change was operationalized as the within-person slope of expectancy across sessions, while baseline expectancy was assessed prior to treatment onset. Linear regressions examined the contribution of baseline expectancy, expectancy change and their interaction to overall symptom improvement, from pre- to post-treatment. Results: A greater increase in expectancy throughout treatment predicted faster and more substantial recovery. Notably, both higher baseline expectancy and greater expectancy change independently predicted better treatment outcomes. Conclusions: These findings highlight that dynamic changes in patients’ outcome expectancy predict overall symptom improvement, independently of baseline expectancy. Integrating these findings within a broader framework of belief-updating in depression, we propose that expectancy change may inform treatment progression and serve as a therapeutic target. Implications for clinical practice and future work are discussed.