Effects of Increasing the Incentive Size in a Longitudinal Study

To assess the possible impacts of increasing the incentive size on response rate and data quality, at one wave of a longitudinal study sample members were randomly assigned to receive one of three incentives: the same 20 incentive per person they had received in previous waves; 30; or 50. Those offered 50 had a higher response rate than those offered 20, and this positive impact persisted for at least the next four waves of biennial data collections. There is some evidence that higher incentives improve data quality as indicated by probabilities of failing to answer questions and of giving responses that would reduce the interview length.