Indicators of retention in remote digital health studies: a cross-study evaluation of 100,000 participants. - Pratap A; Neto EC; Snyder P; Stepnowsky C; Elhadad N; Grant D; Mohebbi MH; Mooney S; Suver C; Wilbanks J; Mangravite L; Heagerty PJ; et al. (NPJ digital medicine, 2020)