Prepayment was superior to postpayment cash incentives in a randomized postal survey among physicians

Objective: Improving response rates, particularly among physicians, is important to minimize nonresponder bias and increase the effective sample size in epidemiologic research. We conducted a randomized trial to examine the impact of prepayment vs. postpayment incentives on response rates. Study Design and Setting: Self-completion postal questionnaires were mailed to 949 physicians who were respondents to an earlier survey and representative of the general physician population in Hong Kong. These physicians were randomly allocated to receive a HK$20 cash prepayment incentive that accompanied the survey (n = 474) or a postpayment reward of the same amount on receipt of the completed questionnaire (n = 475). Results: The final prepayment response rate was 82.9%, compared with 72.5% in the postpayment arm (P <.001). Of the eight alternative incentive and follow-up strategies evaluated, three lie on the efficiency frontier (i.e., not dominated), including postpayment with three mailings at HK$42.7, prepayment with three mailings at HK$66.5 and prepayment with three mailings and telephone follow-up at HK$112.1 per responder recruited (US$1 = HK$7.8). Conclusion: The findings demonstrate that prepayment cash incentives are superior to postpayment of the equivalent amount in improving response rates among a representative sample of Hong Kong physicians. Further research should concentrate on confirming the generalizability of these findings in other health care occupation groups and settings. (C) 2004 Elsevier Inc. All rights reserved.