Use of a Lottery as an Incentive to Increase Survey Participation

This paper describes an experiment in which a chance to win a monetary prize was offered in a contacting letter to a randomly selected half of the women in a survey sample, while the prize was not mentioned in the contacting letter sent to the other half. The prize winners were to be chosen at random from participants in the survey. The survey was designed as a validation study of abortion and was conducted in Tallinn, Estonia in April-May 1992. The sample consisted of 360 women who had a registered abortion during 1991. The lottery acted as a strong incentive for the women in the sample to become respondents. It increased by almost 20 points the percentage who returned a postcard verifying their address and arranging an appointment for the interview. Also, among those who returned the postcard, 93% eventually completed the survey, compared to only 62% among those who did not. The effect of the lottery operated entirely through an increase in the chance that the women in the sample would return the postcard. The lottery had no effect on participation by those who had not first returned the postcard. Nonetheless, the lottery substantially reduced the costs of completing the fieldwork without biasing the survey results. There was no evidence of induced self-selection of those with a strong interest in the announced substantive focus of the survey -- health and medical services -- of a deterioration in response validity: those given the incentive were no more or less likely to report accurately that they had had a recent abortion.