  Digital technologies such as smartphones are transforming the way scientists
conduct biomedical research using real-world data. Several remotely-conducted
studies have recruited thousands of participants over a span of a few months.
Unfortunately, these studies are hampered by substantial participant attrition,
calling into question the representativeness of the collected data including
generalizability of findings from these studies. We report the challenges in
retention and recruitment in eight remote digital health studies comprising
over 100,000 participants who participated for more than 850,000 days,
completing close to 3.5 million remote health evaluations. Survival modeling
surfaced several factors significantly associated(P < 1e-16) with increase in
median retention time i) Clinician referral(increase of 40 days), ii) Effect of
compensation (22 days), iii) Clinical conditions of interest to the study (7
days) and iv) Older adults(4 days). Additionally, four distinct patterns of
daily app usage behavior that were also associated(P < 1e-10) with participant
demographics were identified. Most studies were not able to recruit a
representative sample, either demographically or regionally. Combined together
these findings can help inform recruitment and retention strategies to enable
equitable participation of populations in future digital health research.
