Targeting subjective engagement in experimental therapeutics for digital mental health interventions

Engagement is a multifaceted construct and a likely mechanism by which digital interventions achieve clinical improvements. To date, clinical research on digital mental health interventions (DMHIs) has overwhelmingly defined engagement and assessed its association with clinical outcomes through the objective/behavioral metrics of use of or interactions with a DMHI, such as number of log-ins or time spent using the technology. However, engagement also entails users' subjective experience. Research is largely lacking that tests the relationship between subjective metrics of engagement and clinical outcomes. The purpose of this study is to present a proof-ofconcept exploratory evaluation of the association between subjective engagement measures of a mobile DMHI with changes in depression and anxiety. Adult primary care patients (N = 146) who screened positive for depression or anxiety were randomized to receive a DMHI, IntelliCare, immediately or following an 8-week waitlist. Subjective engagement was measured via the Usefulness, Satisfaction, and Ease of Use (USE) Questionnaire. Across both conditions, results showed that individuals who perceived a mobile intervention as more useful, easy to use and learn, and satisfying had greater improvements in depression and anxiety over eight weeks. Findings support our proposed experimental therapeutics framework that hypothesizes objective/ behavioral and subjective engagement metrics as mechanisms that lead to changes in clinical outcomes, as well as support directing intervention design efforts for DMHIs to target the user experience.