Identifying the active ingredients of a behavioral activation-based digital single-session intervention targeting depression.

Digital single-session interventions (SSIs) have been shown to be effective in reducing myriad mental health conditions. However, it is unclear which components of digital SSIs drive their therapeutic effects. In this study, we divided a well-evaluated behavioral activation-based SSI into three candidate components-PSYCHOEDUCATION, TESTIMONIALS, and ACTION PLAN-each hypothesized to have independent therapeutic value. We conducted a 23 factorial experiment (N=889) to evaluate effects of the individual components on depressive symptoms. Our results showed that only the ACTION PLAN candidate component had a significant main effect on depressive symptoms at 2-week (s.m.d=-0.18) and 8-week (s.m.d=-0.12) follow-ups. Additionally, user's perceptions of the intervention's credibility and their expectations of improvement immediately after completing it were significantly associated with a reduction in depressive symptoms at both time points. Our findings offer a more nuanced understanding of which elements within digital SSIs may drive their therapeutic benefits.