The effect of cash lottery on response rates to an online health survey among members of the Canadian Association of Retired Persons: a randomized experiment.

OBJECTIVES The objectives of the study were 1) to assess the effect of cash lottery on participation rates in a web-based study of physical activity and joint health and 2) to compare recruitment via direct e-mail versus advertisement in an online newsletter. METHODS A sample of 1,150 individuals, randomly selected from a database of members of the Canadian Association of Retired Persons (CARP), was e-mailed a request to participate in an online survey, with follow-up e-mails after 1 and 2 weeks. The sample was randomly split into two groups. Half the sample was offered entry into a cash draw with a $500 grand prize and five $100 prizes, whereas the other half was not offered any incentive. In addition, a brief advertisement about the survey (without an incentive) was placed in an online newsletter that was circulated to 14,000 randomly selected CARP members. RESULTS In the incentive group, 305 (53.0%) clicked on the hyperlink and visited the website and 84 (14.6%) completed the survey. In the group who received no incentive, 280 (48.7%) clicked on the link and 59 (10.3%) completed the survey. Of those who received the online newsletter, 492 (3.5%) visited the website and 106 (0.76%) completed the survey. CONCLUSION A relatively modest financial incentive in the form of a cash lottery significantly increased participation rates in an online health survey. Recruitment through a newsletter advertisement had a very low yield compared to direct e-mail.