Impact of Reminder Strategies on Survey Response in Older Adults: A Randomized Trial in Japan

Abstract Background: Declining postal survey response rates, especially among older adults, threaten research validity. This study evaluated the effectiveness and cost-effectiveness of two reminder strategies—a postcard and a re-sent questionnaire—issued seven months after initial mailing among older Japanese adults. Methods: We conducted a three-arm randomized controlled trial with 1500 adults aged 48–88 years from the Japan Multi-Institutional Collaborative Cohort Chiba cohort. Non-respondents to a survey mailed seven months were randomized equally to: (1) no reminder, (2) reminder postcard, or (3) re-sent questionnaire with prepaid envelope. The primary outcome was response within 60 days. Logistic regression estimated adjusted ORs. Results: Final sample sizes were 492, 486, and 487 participants. Response rates were 0.8% (control), 12.1% (postcard), and 35.5% (re-sent questionnaire) (P < 0.001). Both interventions significantly increased responses, with no evidence of effect modification by age, sex, or educational attainment. Most responses occurred within two weeks. Cost per response was ¥867 for postcards versus ¥503 for re-sent questionnaires. Conclusion: Both reminder strategies significantly improved response rates versus no reminder. The re-sent questionnaire achieved the highest response and best cost-effectiveness, when implemented seven months after the initial mailing. Re-sending questionnaires should be prioritized to enhance participation in surveys targeting aging populations.