Introduction
cognitive behavior, mental ill, anxiety, JITAIs, depression
SECONDARY, DISORDERS, EMA
Approximately one-fifth of young people worldwide are affected by mental ill health [Repetitive negative thinking (RNT) is a key transdiagnostic mechanism that accounts for the overlap between several mental disorders, particularly depression and anxiety [A key shortcoming of existing psychological treatments is the inability to tailor interventions according to person, place, and time. Psychological problems and associated transdiagnostic processes are dynamic, showing a high degree of temporal variability as they unfold from moment to moment in interaction with the internal and external environments [RNT treatments typically involve skills and strategies aimed at disrupting the process as it is happening through techniques such as mindfulness, cognitive restructuring, or problem-solving [Researchers have looked toward smartphone apps as a medium to deliver interventions in daily life, potentially overcoming the therapy–real world gap [Smartphone apps may improve the efficacy of transdiagnostic treatments through their unique capability to detect and respond to momentary changes in transdiagnostic mechanisms in real time using personalized interventions [The opportunity to target transdiagnostic mechanisms in real time using JITAIs is an area with significant potential to improve the personalization, engagement, and effectiveness of psychological interventions. The vast majority of JITAIs have focused on health behaviors, with very little research conducted on targeting key transdiagnostic mechanisms or for application in youth populations [To the best of our knowledge, the potential for JITAIs to provide personalized interventions targeting disruption in transdiagnostic mechanisms in real time and real-world contexts for youth mental health has not yet been explored. To investigate this potential, our group developed a world-first smartphone intervention called “Mello,” a self-guided, personalized, transdiagnostic, and mechanistic smartphone intervention targeting RNT in young people with depression and anxiety. Mello is based on the JITAI model in that intervention strategies designed to disrupt RNT in the moment are tailored based on momentary assessments of relevant contextual variables. Mello does not adopt a single therapeutic modality but rather translates multiple techniques from third- and second-wave cognitive behavior therapies, which have evidence for reducing RNT into brief interventions designed to disrupt RNT in the moment. This was based on the rationale that effective intervention strategies exist across different therapeutic modalities, and consultations with young people and clinicians through the development of Mello clearly highlighted the range of techniques that were used to effectively reduce RNT in the moment. Consistent with the JITAI model of identifying and intervening in moments of need, Mello uses an algorithm that tailors a recommendation for a microintervention designed to disrupt RNT based on responses to a brief EMA check-in that captures the levels of RNT, mood, context, and location.This study was a pilot randomized controlled trial (RCT) comparing Mello with a nonactive control group over a 6-week period. The primary aim was to evaluate the feasibility, acceptability, and estimated efficacy of Mello in reducing RNT, depression, and anxiety in youth with clinical levels of depression and anxiety and increased RNT. Secondarily, the exploratory aims were to evaluate whether the effect of Mello on depression and anxiety outcomes was explained by effects on RNT, as this was the transdiagnostic target of the intervention. Further aims were to evaluate engagement with Mello and the effect of the intervention on the secondary outcomes.