Introduction
RECRUITMENT, RECRUITMENT
Research participants are increasingly approached through digital or remote means to contribute their health data for biomedical discovery and innovation. Digital research studies delivered through a web portal (web-based) or smartphone app (app-based) aim to harness the capabilities and ubiquity of the internet, smartphones, and sensor devices to improve recruitment, engagement, and data collection over time [Recruitment of a representative study population is critical for achieving the goals of precision medicine and ensuring the generalizability of findings [We conducted a broad-based digital recruitment campaign within our health system, sending unsolicited email invitations to over 200,000 patients between August 2015 and February 2016 inviting them to join the Health eHeart Study (a cardiovascular-focused “eCohort” with registration, consent, and ongoing data collection occurring entirely on the internet). Random subsets of the sampling frame received emails on different days, at different times, and with different subject lines to maximize variation in the recruitment outreach strategy. To study the success of our campaign in recruiting different segments of our target population, we evaluated our invited eligible patient cohort at the earliest point of research participation—enrollment—defined by registration and consent into the Health eHeart Study. We obtained electronic health record data from the entire sampling frame and used these data to analyze sociodemographic and clinical characteristics of the patients that predicted Health eHeart Study enrollment and analyzed barriers at each step in the enrollment process, with the goal of learning how email-based recruitment can be used optimally to enroll representative study populations for digital health studies.