Dentists' response to financial incentives in a mail survey of malpractice liability experience

This two-part methodologic research was designed to evaluate the effects of a financial incentive on questionnaire response rate and response bias for general dentists surveyed by mail. Subjects were 517 clinicians randomly selected from a two-state population of practitioners insured by a single malpractice liability carrier. Subjects received a check for either $5 or $10 in the original mailing. In Study 1, a single mailing and postcard follow-up resulted in a 57.8 percent (111/192) response rate. In Study 2, employing Dillman's Total Design Method, a 69.6 percent (208/299) response was obtained after a third mailing. Analysis of response rate by incentive level in each study revealed no significant differences. In contrast, early responders (first mailing and follow-up postcard) differed from late responders (second and third mailings) on age (41.4 vs 37.0 years; T = 2.17; P = .032), non-Caucasians (27.7% vs 63.9%; chi 2 = 17.3; df = 4; P < .002), females (13.9% vs 27.8%; chi 2 = 3.9; df = 1; P < .05), foreign-trained (7.0% vs 19.4%; chi 2 = 16.5; df = 2; P < .001), and dissatisfaction with practice (31% vs 51%; chi 2 = 7.8; df = 4; P = .10). Thus, the magnitude of the financial incentive in this experiment had no differential effect on response rate. But differences in responses from late responders (proxies for nonresponders) on demographic characteristics and key study variables suggest the persistence of response bias despite an acceptable response rate. Future dental health survey research should employ tests for response bias on both sets of variables.