The effect of conducting a lottery on questionnaire response rates: A randomised controlled trial

Aim: To study the effect of a lottery incentive on questionnaire response rate. Material and methods: In Copenhagen County, Denmark, a random sample of 2543 men and women between the ages of 19 and 60 were randomised into a control group and an intervention group. Both groups were contacted by mail and asked to complete a questionnaire on sociodemografic characteristics, self-rated health and self-reported physical activity level. The intervention group was offered participation in a small lottery for returning the questionnaire. No incentive was offered to the control group. Main results: The final response rate for the control group was 60.4 and 63.4% for the intervention group. Although the response rate was significantly higher in the intervention group after 2 and 3 weeks, the difference in the final response rate between groups was not statistically significant (p = 0.12). There was no statistically significant difference between groups in sociodemografic characteristics, self-rated health or self-reported physical activity level. Conclusion: A lottery incentive had no significant effect on the overall response rate, but may have contributed to a quicker response. Furthermore a lottery incentive did not seem to alter the selection of respondents.