Token monetary incentives improve mail survey response rates and participant retention: results from a large randomised prospective study of mid-age New Zealand women.

AIM: To examine if a small token monetary incentive (NZ$5) increases mail survey response rates and participant retention of 40-50 year old New Zealand women. METHOD: In 2009, 2500 women were randomly selected from the New Zealand electoral rolls for a prospective study investigating factors related to the prevention of weight gain. At baseline, 400 women were randomly assigned to receive NZ$5 with the initial survey mail-out in addition to nonmonetary gifts to encourage participation (pen, tea bag, entry in lottery draw) received by all women. At 2 years, 400 women (200 received NZ$5 at baseline and 200 had not) were randomly assigned to receive the same token monetary incentive. At 3 years, all women identifying as an ethnic minority (n=234) and 300 randomly selected women of other ethnicities received the token monetary incentive with the initial mail out. RESULTS: The baseline response rate for women who received NZ$5 was significantly higher than for women who did not (76% vs 64%, p<0.001). At 2 years, retention rate for all women who received NZ$5 was significantly higher than for women who did not (88% vs 80%, p<0.001). At 3 years, among those women not identifying as an ethnic minority, the retention rate for those who received NZ$5 was significantly higher than for those who did not (84% vs 77%, p=0.014). CONCLUSION: Inclusion of a small token monetary incentive significantly increases mail survey response rates and participant retention in mid-age New Zealand women.