Principal Findings
JITAIs [, depression, anxiety
SECONDARY, RECRUITMENT
The aim of this pilot RCT was to evaluate the feasibility, acceptability, and estimated efficacy of a personalized, transdiagnostic, and mechanistic smartphone intervention called Mello for targeting RNT in young people with depression and anxiety. The results showed significantly greater reductions in depression, anxiety, and RNT in those who used Mello compared with an inactive control, with moderate to large effect sizes, suggesting that the app may be effective for treating depression and anxiety in youth with elevated RNT. The secondary aim was to explore whether improvements in depression and anxiety were accounted for by reductions in the target transdiagnostic mechanism of RNT, with exploratory analyses supporting this theoretical mechanism of action. Findings concerning feasibility and acceptability were positive. Recruitment targets were exceeded in the allocated trial timeframe, with 86% (55/64) of identified eligible young people participating in the trial and 95% (52/55) of participants completing all assessments. There was high endorsement of the app among users, with 96% (27/28) reporting that they would recommend the app to others and 71% (20/28) rating it as 4 or 5 stars out of 5. Finally, use statistics showed high levels of sustained engagement with Mello over the intervention period, with young people using the app on average half of all days, and 59% (17/29) of users remaining engaged at week 6. These positive results support the promise of Mello as a potentially effective, engaging, and scalable digital intervention.Systematic reviews have demonstrated generally high levels of acceptability of mental health apps in youth populations across the domains of usability, functionality, and general satisfaction [While contextualizing rates of engagement with Mello relative to the broader field is complex, given challenges in standard measurement [Although a larger trial is needed to confirm the results, the effect sizes show that using Mello led to reductions in depression and anxiety. Our findings suggest that this may occur via the hypothesized mechanism of reducing RNT. If confirmed, these findings support the theory that targeting reductions in transdiagnostic mechanisms will lead to improvements in symptoms [The pattern of effect sizes across outcome measures provides insights into the potential therapeutic mechanisms of Mello. On the basis of a recent meta-analysis [A key feature of Mello, consistent with the design of JITAIs [