Introduction
Digital technologies offer new opportunities to collect epidemiologic data and real-world evidence. Smartphones, smartwatches, and wearables have increasing penetration and use [However, participant retention and engagement is a major challenge in epidemiological and clinical trials deploying surveys or interventions with digital technologies. In the MyHeart Counts Cardiovascular Health Study, there was a rapid drop-off observed in user engagement with app use after approximately 4 days [We conducted a randomized controlled trial to test the effect of smartphone app notification messaging strategies on improving participants’ long-term (3 months) use and return of HR and blood pressure (BP) data. The trial was embedded in the electronic Framingham Health Study (eFHS), an e-cohort of participants from the FHS, using a smartphone app and digital devices [