The effects of lottery incentive and length of questionnaire on health survey response rates: a randomized study.

Maximizing the response rate of self-administered questionnaires is key in survey research. We aimed to evaluate the effects of lottery incentive and length of questionnaire on health survey response rates when used in isolation or combined. A random sample of 440 residents in Western Sydney, Australia was randomly allocated to four equal groups to receive or not receive an instant lottery ticket and a long (seven page) or short (one page) questionnaire. The overall response rate was 71.8%. The final response rates were higher among those receiving the short, rather than the long, questionnaire (75.6% versus 68.2%) (P = 0.08); and among those receiving the lottery incentive compared with those not receiving the incentive (75% versus 68.2%) (P = 0.09). By logistic regression analysis, the success of obtaining a completed questionnaire without any follow-up reminders was significantly associated with the lottery incentive but not the questionnaire length (P = 0.03 and P = 0.54, respectively). The difference between lottery and no lottery groups decreased gradually during the follow-up. A lottery incentive is associated with an increased response after the first mailing. A small up-front cost for a lottery ticket may be worthwhile, since it can save further costs by obviating the need for repeated follow-ups.