Quantifying income-related inequality in healthcare delivery in the United States

Background: Numerous studies have found that high-income Americans use more medical care than their low-income counterparts, irrespective, of medical "need." The methods employed in these studies, however, make it difficult to evaluate differences in the degree of income-related inequality in utilization across population subgroups. In this study, we derive a summary index to quantify income-related inequality in need-adjusted medical care expenditures and report values of the index for adults and children in the United States. Methods: We used the summary index of income-related inequality in expenditures developed by Wagstaff et al.(1) The source of data for the study was the Household Component of the 1996-1998 Medical Expenditure Panel Survey, which contains person-level data on medical care expenditures, demographic characteristics, household income, and a wide array of health status measures. We used multivariate regression analysis to predict need-adjusted annual medical care expenditures per person by income level and used the predictions to calculate the indices of inequality. Separate indices were calculated for all adults, working-age adults, seniors, and children ages 5 to 17. Results: For all age groups, predicted expenditures per person, adjusted for medical need, generally increased as income rose. The index of inequality for all adults was +0.087 (95% confidence interval, +0.03, +0.139); for working-age adults, +0.099 (+0.046, +0.152); for seniors, +0.147 (+0.059, +0.235); and for children, +0.067 (+0.006, +0.128). Conclusions: There exists income-related inequality in medical care expenditures in the United States, and it favors the wealthy. The inequality is highest among seniors despite Medicare, intermediate among working-age adults, and lowest among children.