Comparison of responses to a US 2 dollar bill versus a chance to win 250 US dollars in a mail survey of emergency physicians.

OBJECTIVES: To evaluate whether small monetary incentives improve physicians' responses to surveys. To the best of the authors' knowledge, no one has evaluated emergency physicians' response rate and cost per participant of a small monetary incentive relative to a chance to win a more substantial sum. The authors compared emergency physicians' responses and per-participant costs between a US 2 dollar bill and a 250 US dollars lottery.
METHODS: Two groups of 288 emergency physicians were randomly selected and mailed a survey. Within each group of 288, half received a US 2 dollar bill and the other half received an offer that respondents would be entered into a drawing to win 250 US dollars. Nonresponders received a reminder postcard one week later, and persistent nonresponders received a second mailing of the survey three weeks after the initial mailing.
RESULTS: Of the 576 surveys that were mailed, nine (2%) subjects were ineligible or undeliverable, leaving 567 eligible subjects, of whom 301 (53%) participated in the survey. The US 2 dollar bill had a substantially higher response rate: 170 (56%) of those receiving a US 2 dollar bill participated versus 131 (44%) of those receiving a chance to win 250 US dollars (95% confidence interval = 5% to 22%; p < 0.001). The US 2 dollar bill offer was less expensive per participant than the 250 US dollars offer. The cost of postage and incentives was 997.33 US dollars for 170 participants, or 5.87 US dollars per participant, for the US 2 dollar bill and 979.29 US dollars for 131 participants, or 7.48 US dollars per participant, for the chance to win 250 US dollars.
CONCLUSIONS: Mailing a US 2 dollar bill incentive produces a better response rate with lower cost per participant than offering a chance to win 250 US dollars.