Efficacy of an Unguided, Web-Based Single-Session Intervention for Internalizing Symptoms in Online Participants: Randomized Controlled Trial

Background: The Common Elements Toolbox (COMET) is an unguided digital single-session intervention (SSI) based on the principles of cognitive behavioral therapy and positive psychology. Although unguided digital SSIs have shown promise in the treatment of youth psychopathology, the data are more mixed regarding their efficacy in adults. Objective: This study aimed to investigate the efficacy of COMET-SSI versus a waiting list control in depression and other transdiagnostic mental health outcomes for online participants with a history of psychopathology. Methods: We conducted an investigator-blinded, preregistered [1] randomized controlled trial comparing COMET-SSI (n=409) with an 8-week waiting list control (n=419). Participants were recruited from the online workspace Prolific and assessed for depression, anxiety, work and social functioning, psychological well-being, and emotion regulation at baseline and at 2, 4, and 8 weeks after the intervention . The main outcomes were short-term (2 weeks) and long-term (8 weeks) changes in depression and anxiety. The secondary outcomes were the 8-week changes in work and social functioning, well-being, and emotion regulation. Analyses were conducted according to the intent-to-treat principle with imputation without imputation and using a per-protocol sample. In addition, we conducted sensitivity analyses to identify inattentive responders. Results: The sample comprised 61.96% of women (513/828), with a mean age of 35.75 (SD 11.93) years. Most participants (732/828, 88.30%) met the criteria for screening for depression or anxiety using at least one validated screening scale. A review of the text data suggested that adherence to the COMET-SSI was near perfect, there were very few inattentive respondents, and satisfaction with the intervention was high. However, despite being powered to detect small effects, there were no statistically or clinically significant differences between the conditions in any of the outcomes at any time point, even when focusing on individuals with more severe symptoms. Conclusions: Our results do not support the use of the COMET-SSI in adult online participants. Future work should explore alternate ways of intervening with paid online participants, including matching individuals to SSIs they may be most responsive to.