Effects of E-Mailed Versus Mailed Invitations and Incentives on Response Rates, Data Quality, and Costs in a Web Survey of University Faculty.

This study used random assignment to assess the effects of invitation mode on response rates, costs, and demographic representativeness. Participants were sent a mailed invitation letter and a $2 cash incentive; a mailed invitation letter only; or an e-mailed invitation. Nonresponding faculty received up to two reminders to participate, by e-mail. Response rates were higher for the groups invited using a postal letter, but the inclusion of $2 did not significantly increase the response rates.