Randomized trial of use of incentive to increase the response rate to a mailed survey

Low response rates, especially among health-care professionals, are a common problem in mailed survey research. We conducted a randomized trial to examine the effects of cash incentives on response rates. A total of 3,335 Chinese medicine practitioners were randomized to one of two interventions accompanying a mailed survey - no incentive (n=1,667), and monetary incentives in two levels at HK$20, and HK$30 (n=834 in each group) on receipt of the returned questionnaire. The response rates were higher among those offered incentives than those without (34.7% vs. 28.5%, X²=14.34, p<0.001). but no significant differences were found between incentives at HK$20 and HK$30 (X²=0.16, p=0.69). Although offered incentives can increase response rates, no incentive was the most cost-effective, in terms of cost per respondent (HK$21.90 per respondent). However, this study focuses on CMPs, the findings may not represent the response rate for all health-care professions in Hong Kong. In fact, the largest population in the health care system in Hong Kong is nurses. Therefore, we cannot conclude that a money enclosure would have been more effective for all health-care professionals. Also, further systematic study of the effects of different incentive strategies in other related research should be encouraged.