Design and Performance of an Email-Based Patient Recruitment Campaign in Primary Care Research: Formative Secondary Analysis.

Background: Recruiting patients in primary care research remains challenging due to clinical workload, staffing constraints, and the need to limit disruption to routine care. Traditional recruitment methods often place a substantial burden on clinics, prompting research teams to adopt low-burden and scalable approaches such as email-based recruitment. Despite its growing use, limited empirical evidence describes how email recruitment campaigns are designed and how they perform when targeting primary care patients in real-world settings. Objective: This study aims to descriptively examine engagement metrics from an email recruitment campaign targeting primary care patients. Methods: We conducted a formative, descriptive secondary analysis of engagement metrics generated during a large-scale email recruitment campaign conducted as part of the Quebec component of the Patient-Reported Indicator Survey-Organisation for Economic Co-operation and Development survey. Between June 2023 and January 2024, a total of 12 primary care clinics invited eligible adult patients (aged ≥45 years) to complete an online survey using a standardized email template distributed via an email marketing platform. Collected engagement metrics included delivery rates, open rates, click-through rates, conversion rates, and device type. Analyses were descriptive and conducted at the clinic level. Results: For 15,277 patients, invitations were successfully delivered to 14,758 (96.6%). The mean open rate for the initial invitation was 73.4% (10,828/14,757; range 57%-88%), decreasing with reminders. Most emails were opened on computers (25,868/30,279, 85.4%). Out of a total of 445 emails, 42 (9.4%) were undelivered due to technical issues, and 403 (90.6%) were undelivered due to incorrect email addresses. The overall conversion rate was 9.7% (1430/14,758). Click-through rates varied by content, with the highest engagement observed for the survey link and lower engagement for supplementary video materials. Reminder emails substantially increased survey participation across clinics (759/1138, 66.7%). Participants who completed the questionnaire were predominantly aged 60 to 69 years, identified as female, and had completed postsecondary education. Conclusions: This formative analysis suggests that email-based recruitment is a feasible and low-burden approach for engaging primary care patients in research. Engagement metrics offer valuable insights at the implementation level to inform the design, adaptation, and monitoring of digital recruitment strategies in real-world primary care settings. These findings provide practical, implementation-oriented insights to inform the design, refinement, and evaluation of email recruitment campaigns in primary care research.