Does treatment preference affect outcome in a randomized trial of a mindfulness intervention versus cognitive behaviour therapy for social anxiety disorder?

Research suggests that treatment preference may affect outcome of randomized clinical trials, but few studies have assessed treatment preference in trials comparing different types of psychosocial interventions. This study used secondary data analysis to evaluate the impact of treatment preference in a randomized trial of a mindfulness-based intervention adapted for social anxiety disorder (MBI-SAD) versus cognitive behaviour group therapy (CBGT). Ninety-seven participants who met DSM-5 criteria for SAD were randomized. Prior to randomization, twice as many participants expressed a preference for the MBI-SAD over CBGT. However, being allocated or not to one's preferred treatment had no impact on treatment response. Additionally, with the exception of perception of treatment credibility, treatment matching had no impact on treatment-related variables, including treatment initiation, session attendance, homework compliance, satisfaction with treatment and perception that treatment met expectations. In sum, despite the greater preference for the mindfulness intervention in this sample of participants with SAD, we found little evidence of preference effects on our study outcomes. Findings should be viewed as preliminary and require replication.