Credibility and expectations: Important factors for understanding clinical response, treatment completion, and dropout in internet-delivered psychological interventions.

Several large studies have identified perceptions of treatment credibility and treatment outcome expectations as potential moderators of treatment response in internet-delivered psychological treatment. However, no studies have specifically focused on these two constructs and their potential roles in the moderation of treatment-related change, treatment completion, or study dropout. Adult samples were derived from four large randomized controlled trials examining internet-delivered treatment for symptoms of depression (n = 445), generalized anxiety (n = 454), social anxiety (n = 486), and panic disorder (n = 292). In these studies, relevant symptom measures were administered at pretreatment and posttreatment, and credibility and expectancy were assessed in Week 2 after participants had had some experience with treatment. Treatment credibility and outcome expectations were relatively high overall, with a majority of participants scoring in the upper ranges. Both variables significantly moderated treatment response across all symptom domains. Specifically, each 1-point increase in either average credibility scores or average expectancy scores were associated with a 5%-8% reduction in symptoms at posttreatment. Higher treatment credibility and outcome expectations were also significantly associated with increased treatment completion and lower rates of study dropout or missingness. The findings suggest that perceptions of treatment credibility and outcome expectancies are important factors in understanding treatment engagement and response to internet-delivered interventions. (PsycInfo Database Record (c) 2025 APA, all rights reserved).