The effect of a voucher incentive on a survey response rate in the clinical setting: a quasi-randomized controlled trial

Dawid Pieper, Nina Kotte, Peggy Ober

Financial rewards have been shown to be an important motivator to include normal healthy volunteers in trials. Less emphasis has been put on non-healthy volunteers. No previous study has investigated the impact of a voucher incentive for participants in a cross-sectional study in a clinical setting. The objective of this study was to examine the impact of a small voucher incentive on a survey response rate in a clinical setting at the point-of-care in a quasi-randomized controlled trial (q-RCT). This was an ancillary study to a survey of patients subsequent to their appointment with a physician investigating physician-patient communication. We randomized participants to receive or not receive a voucher for a coffee (costs: 1 €) enclosed in the survey package. Alternation of groups was performed on a weekly basis. The exact Chi-square test was used to compare response rates between study arms. In total, 472 participants received the survey package. Among them, 249 participants were quasi-randomized to the voucher arm and 223 to the control group. The total response rate was 46%. The response rates were 48% in the voucher arm and 44% in the control group. The corresponding risk ratio was 1.09 (95% CI: 0.89, 1.32). A small voucher incentive to increase the response rate in a survey investigating physician-patient communication was unlikely to have an impact. It can be speculated whether the magnitude of the voucher was too low to generate an impact. This should be further investigated in future real-world studies.