Characteristics Associated With the Use of the Mindfulness Meditation App Headspace in a Large Public Health Deployment: Cross-Sectional Survey Study - Judith Borghouts; Elizabeth V Eikey; Cinthia De Leon; Stephen M Schueller; Margaret Schneider; Nicole A Stadnick; Kai Zheng; Dana B Mukamel; Dara H Sorkin (JMIR Formative Research)