Effects of incentive size and timing on response rates to a follow-up waveof a longitudinal mailed survey

Young adults who had previously participated in a longitudinal survey of yo uth were sent a questionnaire, They were randomly assigned to receive a $20 prepayment, a $20 postpayment, or a $25 postpayment for participation in t he latest survey. Those in the large incentive condition were 7 percentage points more likely to return a survey than those in the smaller postpayment group. Prepayment had a smaller less reliable effect. Effects of incentive magnitude and timing were consistent at each,month of the study period; on ly better high school grades distinguished early responders from late respo nders. Nonresponders had characteristics suggestive of low social conformit y and were more likely than responders to be African American and male and have low SES. The discussion centers on motivations for participating in re search and differences in the incentives likely to promote continued respon se versus initial study enrollment.