DENTISTS RESPONSE TO FINANCIAL INCENTIVES IN A MAIL SURVEY OF MALPRACTICE LIABILITY EXPERIENCE

This two-part methodologic research was designed to evaluate the effec ts of a financial incentive on questionnaire response rate and respons e bias for general dentists surveyed by mail. Subjects were 517 clinic ians randomly selected from a two-state population of practitioners in sured by a single malpractice liability carrier Subjects received a ch eck 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) r esponse rate. In Study 2, employing Dillman's Total Design Method, a 6 9.6 percent (208/299) response was obtained after a third mailing. Ana lysis of response rate by incentive level in each study revealed no si gnificant differences. In contrast, early responders (first mailing an d 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%, chi2=17.3; df=4; P<.002), females (13.9% vs 27.8%; c hi2=3.9; df=1; P<.05), foreign-trained (7.0% vs 19.4%; chi2=16.5, df=2 , P<.001), and dissatisfaction with practice (31% vs 51%; chi2=7.8; df =4; P=.10). Thus, the magnitude of the financial incentive in this exp eriment had no differential effect on response rate. But differences i n responses from late responders (proxies for nonresponders) on demogr aphic characteristics and key study variables suggest the persistence of response bias despite an acceptable response rate. Future dental he alth survey research should employ tests for response bias on both set s of variables.