Income-Related Inequalities in Obesity and Disability in the United States, 1985-2004
Posted: 22 Jun 2007
BACKGROUND: Elimination of health disparities is one of the two overarching goals of the Healthy People 2010 initiative of the U.S. Department of Health and Human Services. If these disparities are derived from such factors as income distribution that might be amenable to policy regulation, the health inequalities might be deemed unjust or inequitable. However, only two studies report such measures for the United States, and none have performed intertemporal comparisons. For an aging population experiencing widening income gaps, measuring the extent to which socioeconomic differences might be contributing to inequalities in health outcomes is critical. Given concerns regarding rising obesity prevalence and its consequent impact on disability, assessing the socioeconomic dimension in these twin trends might be an essential first step.
OBJECTIVE: To determine levels and changes in income-related inequalities in obesity and disability status among the U.S. adult population, over time, and across demographic groups.
DATA: U.S. National Health Interview Surveys for 1985-2004.
METHODS: Any reported limitation in age-appropriate activities is used for measuring disability. A body mass index (BMI) > 30.0 is used for defining obesity, with BMI estimated from self-reported height and weight. The concentration index (CI) is used to measure income-related inequality in obesity and disability among adults aged >18 years. The index can range from -1 to +1, indicating whether ill health is concentrated among the poorest (CI < 0), richest (CI > 0), or is equally distributed (CI = 0) by family income. CIs are computed from individual-level data for the overall population, as well as for groups stratified by age, race, and sex to estimate the inequality within demographic groups. Standard errors of CIs are calculated to test whether the indices are statistically different from zero. Finally, the indices are compared to identify change over time and across subgroups.
RESULTS: All indices are negative and statistically significant, indicating that income-related inequalities in both obesity and disability favor the higher income groups. However, although the prevalence of obesity has been rising rapidly, income-related inequalities in obesity, although statistically significant, are small and declining over time. In contrast, although disability rates demonstrate little change during the past two decades, income-related inequalities in disability are substantial, significant, and increasing over time. Temporal patterns similar to the overall population are observed among all age, sex, and race groups. When compared across groups, income-related inequalities in obesity are greatest for those aged 35-49 years, high among women but low or not significant for men, and slightly greater among whites compared with blacks. Income-related inequalities in disability are similar in magnitude for men and women and more pronounced among blacks than among whites.
CONCLUSIONS: Income-related inequalities in obesity are and declining over time. The reasons for the diminishing influence of income differences deserve further exploration. In contrast, income-related inequalities in disability status are statistically significant and increasing over time. Subsequent analysis on the relationship between income distribution and health might help gauge whether income-transfer programs are pertinent policy tools for narrowing disparities in disability status.
Keywords: health inequality, obesity, disability, concentration index
JEL Classification: D63, I12, I18
Suggested Citation: Suggested Citation