To describe the recruitment approach in a large-scale, virtual, observational study of brain health.

Decentralized trials using digital devices for data collection offer new recruitment opportunities compared to traditional site-based studies.  Digital strategies greatly expand reach and accessibility to broader populations, however, not without introducing self-selection bias for individuals facile with consumer technology.  

INTUITION (NCT05058950) is a two-year observational study of 23,000 US-based participants, using remote-data collection with a study-specific app, iPhone, and Apple Watch. Recruitment tactics included: (i) electronic and traditional word-of-mouth referral by participants, (ii) social media advertisements and search engine results, (iii) email outreach, (iv) community health and advocacy events, and (v) study website and App Store traffic. At regular intervals, we evaluated performance for each recruitment strategy and shifted resources to optimize ongoing recruitment to attain demographic heterogeneity. 

3 key findings emerged from the recruitment strategy. First, the decentralized design lowered traditional barriers to participation and expedited enrollment. Within 12-months, over 50,000 individuals from all 50 states downloaded the study app and consented with 42% of those completing enrollment. This suggests a broad willingness to participate in virtual research.  Second, the technology and device eligibility criteria did not prevent enrollment of a heterogenous study population, in terms of age (range: 21-86 years, median: 62.8), sex (64.8% female), race/ethnicity (24% non-Caucasian), education (33.8% with educational attainment below college degree), income (22.1% < US$50k annual), and cognitive health (17.1% with cognitive complaints/impairment). Third, the most successful recruitment tactics were family and friend referrals and focused email campaigns, which consistently outperformed tactics through social media and paid search channels. 

INTUITION expeditiously enrolled a large, heterogenous adult population with a multi-faceted recruitment strategy which could adjust to ongoing performance feedback. Word-of-mouth and email outreaches that focused on demographic diversity emerged as the most efficient tactics.