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

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.

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.

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.

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.