Treatment Credibility as a Mechanism of Change in Cognitive- Behavioral Therapy: Effects on Depression and Anxiety

Objective: This study aimed to provide evidence for treatment credibility (TC) as a potential mechanism of change in cognitive-behavioral therapy (CBT). Therefore, it focused on within-person effects which are free of the influence of stable characteristics and thus allow to exclude certain alternative explanations for the association under study. Method: The sample included 1,423 patients receiving outpatient CBT, who presented a wide variety of psychiatric diagnoses (mostly affective and anxiety disorders). TC, depression, and anxiety were measured every fifth session from session 5 to 25 using the Credibility Expectancy Questionnaire (CEQ), the Patient Health Questionnaire-9 (PHQ-9), and the General Anxiety Disorder-7 (GAD-7), respectively. Symptom severity was assessed every session using the HSCL-11. Within- and between-person effects of TC, depression and anxiety were analyzed using the Latent Curve Model with Structured Residuals (LCM-SR). In exploratory analyses, within-person effects of TC on next-session symptom severity were assessed using a modification of the LCM-SR. Results: LCM-SRs exhibited excellent fit in main analyses. There were significant negative correlations of both intercepts and slopes (between-person level) of CEQ and PHQ-9 as well GAD-7. No significant cross-lagged effects (within-person level) were found over the 5-session interval. However, session-wise analyses revealed significant cross-lagged effects of CEQ on HSCL-11. Conclusions: This study is the first to find significant within-person effects of TC in session-wise analyses. This lends preliminary support to the notion of TC as a mechanism of change. The lack of significant findings at the 5-session interval is discussed considering the specific design used in this study.