Predictors of Patient Adherence to Cognitive-Behavioral Therapy for Obsessive-Compulsive Disorder

ment using the Readiness Ruler [3] . These measures were completed after the 3 introductory sessions and before exposure sessions began. We also examined baseline characteristics that predicted EX/RP outcome in prior OCD studies [14] . These included depressive severity as measured by the 17-item Hamilton Depression Rating Scale [15] , insight on the Brown Assessment of Beliefs Scale [16] , quality of life as measured by the Quality of Life and Enjoyment Questionnaire [17] , Axis I comorbidity using the SCID-I [18] , total number of serotonin reuptake inhibitor trials, female gender, employment status, work impairment as measured by an item on the Sheehan Disability Scale [19] , and hoarding subtype. Simple linear regression examined potential bivariate predictors of adherence. Significant predictors (p ! 0.05) were then considered in subsequent mediation analyses (using Mplus 6.1) that involved simultaneous multiple regressions of adherence on all predictors and of treatment outcome (measured by post-treatment Y-BOCS adjusting for baseline Y-BOCS) on all predictors and adherence. Significant predictors (p ! 0.05) of adherence and outcome in these multiple regressions were retained and their indirect effects (mediation effects) on treatment outcome through adherence were estimated and delta method standard errors were used for 95% confidence intervals and testing [20] . Data from all patients having a PEAS score were used (n = 28) and full information maximum likelihood was implemented in Mplus to account for missing post-treatment Y-BOCS scores (3 subjects dropped out from EX/RP treatment after session 9). Estimates were standardized to facilitate interpretation across predictors with different units. The relationship between potential predictors and patient adherence to between-session EX/RP assignments based on simple regressions is presented in table 1 . The 6 significant (p ! 0.05) bivariate predictors of patient adherence were entered into mediation analyses and their estimated indirect effects are presented in table 1 . Therapeutic alliance (WAI-SR, beta = 0.53), treatment readiness (Readiness Ruler, beta = 0.38), and hoarding status (beta = –0.26) all had significant (p ! 0.05) independent effects on patient adherence. Patient adherence also had a significant direct effect (beta = –0.57, p ! 0.01) on outcome and significantly mediated the impact of these other predictors on post-treatment OCD severity ( table 1 , indirect effects). The effects for treatment expectancy and readiness to change (URICA) were not significant in these mediation analyses. Work impairment (Sheehan Disability Scale) was not significantly associated with patient adherence, although it directly predicted post-treatment OCD severity (0.40, p ! 0.01). Our findings have several implications. First, therapeutic alliance (measured by the WAI-SR) predicted treatment outcome through its impact on patient adherence. The WAI-SR assesses patient attitudes about EX/RP strategies and goals presented by the therapist, and patients’ trust in the therapist. This suggests that taking time to understand patients’ symptoms and to careCognitive-behavioral therapy consisting of exposure and response prevention (EX/RP) is an effective treatment for obsessivecompulsive disorder (OCD). However, only about half of patients achieve minimal or no symptoms by the end of treatment [1–3] . Identifying factors that lead to poor outcome and developing interventions to address them is one way to maximize the effects of EX/RP. Patient adherence to EX/RP is a strong predictor of EX/ RP outcome [4, 5] . Specifically, during EX/RP treatment, therapists teach patients to face feared situations and thoughts (exposures) and to refrain from compulsive behaviors (response prevention). However, no prior study has systematically examined what predicts patient adherence to EX/RP procedures. We examined potential predictors of patient adherence to EX/ RP and whether patient adherence mediated the relationship between these predictors and post-treatment OCD severity. The sample consisted of 28 adults (18–70 years old) with OCD who received EX/RP as part of a clinical trial described in detail elsewhere [3] . In brief, patients participated in 8 weeks of EX/RP that included 3 introductory sessions and 15 twice-weekly 90-minute exposure sessions following the guidelines of Kozak and Foa. Patient adherence was measured at each exposure session using the Patient EX/RP Adherence Scale (PEAS) [7] ; it assessed the quantity and quality of between-session exposures and the degree of response prevention practiced for homework. OCD symptoms were rated by independent evaluators using the YaleBrown Obsessive-Compulsive Scale (Y-BOCS) [8, 9] . We examined four factors hypothesized to affect cognitive-behavioral therapy adherence in other patient groups [3, 10–12] : treatment expectancy using the Expectancy Questionnaire [10] , therapeutic alliance using the Working Alliance Inventory – Self Report (WAI-SR) [12] , readiness for change using the University of Rhode Island Change Assessment (URICA) [13] , and readiness for treatReceived: March 25, 2011 Accepted after revision: June 22, 2011 Published online: February 2, 2012