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.


METHODS
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 dollar 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 dollar 42.7, prepayment with three mailings at HK dollar 66.5 and prepayment with three mailings and telephone follow-up at HK dollar 112.1 per responder recruited (US dollar 1=HK dollar 7.8).


CONCLUSIONS
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.
Department of Community Medicine, Faculty of Medicine, University of Hong Kong, Building 21, Sassoon Road, Hong Kong, People's Republic of China.
Gabriel M
GM
Leung
Janice M
JM
Johnston
Hnin
H
Saing
Keith Y K
KY
Tin
Irene O L
IO
Wong
Lai-Ming
LM
Ho
D001291:Attitude of Health Personnel; D003362:Cost-Benefit Analysis; D005260:Female; D006723:Hong Kong; D006801:Humans; D008297:Male; D009042:Motivation; D010820:Physicians / Q000523:psychology*; D012051:Reimbursement Mechanisms / Q000191:economics / Q000458:organization & administration; D015983:Selection Bias; D011795:Surveys and Questionnaires / Q000191:economics*