Response rates and representativeness: a lottery incentive improves physician survey return rates

To test the effect of a AU dollars 2 scratch lottery ticket on response rates to a national mailed questionnaire of Australian general practitioners (GPs) and medical specialists.

A randomized controlled trial was conducted and the incentive sent to half of the participants with the first mailing. A single follow-up mailing without incentive was sent to all non-respondents. Survey respondents were then informed of the research question regarding incentives and allowed to withdraw their study data. Differences in response rates between doctors receiving and not receiving the incentive, and between respondents and non-respondents, were examined.

The overall response rate was 47% (443 respondents). Twenty-two respondents (5%) withdrew their data after being informed of the research question. Of the remaining 421 respondents, 233 had received the incentive (response rate 49.7%) and 188 had not (40.1%, p=0.0032). The absolute increase in response rate with the incentive (9.6%, 95%CI 3.2, 15.9) was quantitatively similar in effect to the reminder mailing (11.8%). The incentive had a larger effect among the GP sample compared with specialists (13.4 vs. 5.9%), although the difference was not statistically significant (p=0.20). There were no systematic differences in demographic characteristics between respondents and non-respondents.

Increased response rates associated with a small incentive may reduce the need for a second mailed reminder, but strong views about the use of incentives may negatively influence the participation of some practitioners. While the overall response rate was low, there was no evidence of bias in our sample.