Effect of a monetary incentive on response to a mail survey

We assessed the effect of a $1 incentive on response to a two-page questionnaire which was sent to 8356 female cosmetologists between 22 and 36 years old. The study population was randomly assigned to one of three groups in which a $1 incentive was enclosed with either the first or second mailing, or with none of the mailings. Ten percent of questionnaires were returned by the postal service because of an incorrect address or death of the addressee and were omitted from response calculations. Of the remaining questionnaires, 79% were completed and returned after up to three mailings. The cumulative response was highest among cosmetologists who received a $1 incentive with the first mailing, (81%; 95% confidence interval (CI), 80 to 82), intermediate among those who received $1 with the second mailing (78%, 95% CI, 77 to 79), and lowest among cosmetologists who received no incentive (74%; 95% CI, 70 to 78). Characteristics of cosmetologists who responded after having received a "41 incentive were similar to those who responded without having received an incentive. The higher costs per response incurred by the use of an incentive must be weighed against the benefit of higher response.