Social phobia moderates the outcome in the EVIDENT study: A randomized controlled trial on an Internet-based psychological intervention for mild to moderate depressive symptoms

Objective: Data from the EVIDENT trial were reanalyzed to examine whether specific anxiety-related comorbidities moderate the effect of an Internet intervention on depression outcome. Method: The EVIDENT study is a randomized controlled trial that included N = 1,013 participants with mild to moderate depressive symptoms (i.e., scores between 5 and 14 on the Patient Health Questionnaire-9 [PHQ-9]) who were randomized to a control group with access to care-as-usual (n = 504) or to an intervention group, which accessed the Internet intervention Deprexis adjunctively to care-as-usual (n = 509). Anxiety-related comorbidities (generalized anxiety disorder, social phobia, panic disorder, agoraphobia, panic disorder with agoraphobia, specific phobia, posttraumatic stress disorder, obsessive-compulsive disorder) were assessed with the Web Screening Questionnaire at baseline. Multilevel models were performed. Results: Twelve potential moderators (8 specific anxiety-related comorbidities, depression severity, and 3 previously identified moderators in the EVIDENT trial) were examined within 1 multilevel model, and only social phobia moderated the intervention effect on depression outcome (in favor of Deprexis). This moderating effect of social phobia did not depend on the other moderators' being included in the model. These results emerged for continuous PHQ-9 scores as well as for clinically important PHQ-9 changes as outcome (p < .05). However, moderating effects did not reach small effect sizes, accounted for less than 1% of the variance in change in depressive symptoms, and showed limited reproducibility in randomly selected split halves. Conclusions: Deprexis appears to be most effective for participants with mild to moderate depressive symptoms and comorbid social phobia, but further replications of this finding are necessary.