A randomized controlled trial to assess the effect of timing of incentive payments on response rates for cohort study telephone interviews

Abstract

Telephone interviews are commonly used to collect longitudinal data from patients presenting to primary care. Maximizing the response rate of telephone interview is important in survey research. Objective: This study examined the effect of the timing of incentive payments on the response rate of telephone interviews conducted at baseline and 1-year for a longitudinal cohort study in primary care. Design: single-blinded randomized controlled trial with cost-effective analysis. Setting: The study was conducted across two primary care settings in Hong Kong, namely general outpatient clinics and nurse-led continence clinics. Patients: Primary care patients with lower urinary tract symptoms were surveyed longitudinally. They were contacted to complete telephone interview two weeks after consent (baseline) and again at 1 year after baseline. 720 subjects were randomly allocated to two equal groups. One group of subjects was given an incentive voucher immediately following consent to participate. The other group was given incentive vouchers only after they completed their 1-year follow-up telephone interview. Outcomes: (i) the baseline and 1-year follow-up response rates and (ii) the cost per subject. Results: there was no statistical difference in response rate at baseline between two groups (71.9% versus 72.2%) (P=0.938). The 1- year follow-up telephone is still ongoing. Conclusion: Whether subjects are given their incentive vouchers immediately or delayed until after study completion does not significantly affect the response rate of telephone interview at baseline. If there is also no significant difference in response rates at the 1-year follow-up time point, incentives should be given at the time when patients give consent to save the cost of postage and minimize the administrative-related burden.