Messaging Modality and Content for Recruitment of Research Participants: A Randomized Clinical Trial.

Importance: Optimizing participant recruitment is critical to the success and generalizability of clinical research, yet there is limited randomized clinical trial evidence comparing the effects of digital recruitment strategies and message framing on participant engagement. Objective: To determine the impact of various recruitment strategies on engagement with potential research participants. Design, Setting, and Participants: This randomized clinical trial was embedded within the Research for Personalized Cardiovascular Disease Prevention (RESILIENCE) study and had a 2 × 2 factorial design. This component of the RESILIENCE study was exclusively virtual and completed online within a single large academic health system in the United States. Potential research participants were identified through electronic health records. The study recruited participants between September 2019 and March 2022, with the analysis undertaken in July to December 2025. No follow-up was undertaken for this study. Interventions: Participants were randomized to a recruitment modality (email vs patient portal) and to a type of message content (altruistic vs individualistic). Main Outcomes and Measures: The primary outcome was participant interest, defined as logging onto the study website by clicking the link in the message within 6 months. A robust log-linear Poisson model was used to estimate the relative risk (RR) of the primary outcome based on modality and message content. Results: Of 15 376 potential research participants (9309 [60.5%] female) identified through the electronic health records, 7737 (50.3%) were randomized to the email recruitment modality and 7639 (49.7%) were randomized to the patient portal modality; 7682 (50.0%) received an altruistic recruitment message and 7694 (50.0%) received an individualistic recruitment message. The primary outcome occurred in 1220 participants (7.9%). The email recruitment modality led to a higher likelihood of the primary outcome than patient portal messages (768 [9.9%] vs 452 [5.9%]; RR, 1.68; 99% CI, 1.45-1.95), while no difference was observed by message content type (634 [8.3%] altruistic vs 586 [7.6%] individualistic; RR, 1.08; 99% CI, 0.94-1.25). There was no significant interaction between message modality and content. Exploratory interactions by age and risk phenotype were observed, with altruistic messaging more effective than individualistic messaging in those aged 60 years and younger and email more effective than patient portal in those older than 60 years and in individuals with obesity. Conclusions and Relevance: In this randomized clinical trial of recruitment strategies, email messaging led to higher participant interest than patient portal messaging, particularly in older individuals. Message content did not significantly impact engagement overall, but altruistic messaging was more effective in younger participants. These results can inform recruitment strategies for future trials. Trial Registration: ClinicalTrials.gov Identifier: NCT04551872.