Examining dental expenditure and dental insurance accounting for probability of incurring expenses

Abstract

Objectives: There are few studies of dental service expenditure in Australia. Although dental insurance status is strongly associated with a higher probability of dental visiting, some studies indicate that there is little variation in expenditure by insurance status among those who attend for care. Our objective was to assess the overall impact of insurance on expenditures by modelling the association between insurance and expenditure accounting for variation in the probability of incurring expenses, that is dental visiting. Methods: A sample of 3000 adults (aged 30–61 years) was randomly selected from the Australian electoral roll. Dental service expenditures were collected prospectively over 2 years by client-held log books. Questionnaires collecting participant characteristics were administered at baseline, 12 months and 24 months. Unadjusted and adjusted ratios of expenditure were estimated using marginalized two-part log-skew-normal models. Such models accommodate highly skewed data and estimate effects of covariates on the overall marginal mean while accounting for the probability of incurring expenses. Results: Baseline response was 39%; of these, 40% (n = 438) were retained over the 2-year period. Only participants providing complete data were included in the analysis (n = 378). Of these, 68.5% were insured, and 70.9% accessed dental services of which nearly all (97.7%) incurred individual dental expenses. The mean dental service expenditure for the total sample (those who did and did not attend) for dental care was AUS$788. Model-adjusted ratios of mean expenditures were higher for the insured (1.61; 95% CI 1.18, 2.20), females (1.38; 95% CI 1.06, 1.81), major city residents (1.43; 95% CI 1.10, 1.84) and those who brushed their teeth twice or more a day (1.50; 95% CI 1.15, 1.96) than their respective counterparts. Conclusion: Accounting for the probability of incurring dental expenses, and other explanatory factors, insured working-aged adults had (on average) approximately 60% higher individual dental service expenditures than uninsured adults. The analytical approach adopted in this study is useful for estimating effects on dental expenditure when a variable is associated with both the probability of visiting for care, and with the types of services received.