Inequalities in Health-related Quality of Life in the United States, 1985-2015

Background: The overarching objectives of the Healthy People 2020 initiative by the U.S. Department of Health and Human Services include: achieving health equity, eliminating disparities, and improving the health of all groups. Consequently, the focus of public health policy has been on improving average health of all groups, thereby reducing inequalities between these groups. However, if within-group inequalities are substantial, then reducing between-group inequalities alone might fall short of welfare improvement, which requires that less healthy individuals experience greater improvement in health than healthier individuals.

Objective: To assess both average health and health inequalities among the U.S. adult population aged 18-69 years, over time, and across demographic and socioeconomic groups.

Data: National Health Interview Surveys (NHIS), 1985-2015.

Methods: Health inequality is measured using the general entropy measures developed in the income inequality literature in economics, as these methods allow statistical decomposition of health inequality in a population into inequalities between-groups and within-groups. Additional indices are also computed to test for sensitivity of the results. Since the approach requires that each individual be assigned a cardinal health outcome, the Health and Activity Limitation Index (HALex), a summary measure of health-related quality of life, is estimated using information on activity limitation and self-perceived health from the NHIS. Average HALex and its inequality indices are computed from individual-level data over time, for the overall population, as well as for groups stratified by age, sex, race and family income.

Results: Although no clear trends can be discerned in average health or health inequality for the overall population, or among subgroups, the share of within-group inequalities in overall inequality is increasing over time. Comparisons across age groups indicate that average health is lower and health inequality higher among the older cohorts. Average health is also lower and health inequality higher among females compared to males. Comparisons by race indicate that average health is lowest and health inequality highest for American Indian/Alaskan Natives, followed by blacks, then whites, and then Asian/Pacific Islanders. Comparisons across income groups indicate that average health is higher and health inequality lower among higher income groups. The decomposition analysis indicates that race explains about 0.5% to 1.5% of the total health inequality while sex accounts for about 0.1% to 0.7%. Income explains 5.5% to 7.5% of health inequality, and age explains 5.5 to 22.5% of inequality. Together, age, sex race and income explain 13.5% to 35% of total health inequality.

Conclusion: Eliminating health disparities between groups defined by age, sex, race, and income might reduce only a small proportion of the overall health inequality in the population. In addition, since low average health in a group is associated with high inequality within the group, elimination of health disparities may not be attainable without reducing within-group inequalities.