Abstract and Introduction
Abstract
Objectives. To examine the association between income inequality and the risk of mortality and readmission within 30 days of hospitalization.
Design. Retrospective cohort study of Medicare beneficiaries in the United States. Hierarchical, logistic regression models were developed to estimate the association between income inequality (measured at the US state level) and a patient’s risk of mortality and readmission, while sequentially controlling for patient, hospital, other state, and patient socioeconomic characteristics. We considered a 0.05 unit increase in the Gini coefficient as a measure of income inequality.
Setting. US acute care hospitals.
Participants. Patients aged 65 years and older, and hospitalized in 2006-08 with a principal diagnosis of acute myocardial infarction, heart failure, or pneumonia.
Main Outcome Measures. Risk of death within 30 days of admission or rehospitalization for any cause within 30 days of discharge. The potential number of excess deaths and readmissions associated with higher levels of inequality in US states in the three highest quarters of income inequality were compared with corresponding data in US states in the lowest quarter.
Results. Mortality analyses included 555,962 admissions (4348 hospitals) for acute myocardial infarction, 1,092,285 (4484) for heart failure, and 1,146,414 (4520); readmission analyses included 553,037 (4262), 1,345,909 (4494), and 1,345,909 (4524) admissions, respectively. In 2006-08, income inequality in US states (as measured by the average Gini coefficient over three years) varied from 0.41 in Utah to 0.50 in New York. Multilevel models showed no significant association between income inequality and mortality within 30 days of admission for patients with acute myocardial infarction, heart failure, or pneumonia. By contrast, income inequality was associated with rehospitalization (acute myocardial infarction, risk ratio 1.09 (95% confidence interval 1.03 to 1.15), heart failure 1.07 (1.01 to 1.12), pneumonia 1.09 (1.03 to 1.15)). Further adjustment for individual income and educational achievement did not significantly attenuate these findings. Over the three year period, we estimate an excess of 7153 (2297 to 11,733) readmissions for acute myocardial infarction, 17,991 (3410 to 31,772) for heart failure, and 14, 127 (4617 to 23,115) for pneumonia, that are associated with inequality levels in US states in the three highest quarters of income inequality, compared with US states in the lowest quarter.
Conclusions. Among patients hospitalized with acute myocardial infarction, heart failure, and pneumonia, exposure to higher levels of income inequality was associated with increased risk of readmission but not mortality. In view of the observational design of the study, these findings could be biased, owing to residual confounding.
Introduction
Income inequality, or the degree to which income is unevenly distributed within a society, peaked in the United States in the late 1920s, declined sharply after the second world war, and has risen steadily since the early 1980s. Many studies, conducted in the US and elsewhere, have documented an association between increased levels of inequality and worsened self reported health status, raised mortality rates, and reduced life expectancy.
Two mechanisms have been posited to explain these associations. A “compositional” explanation suggests that the poor health outcomes can be attributed to the increased rates of poverty typically found in highly unequal societies. A complementary “contextual” explanation posits that a high level of inequality has corrosive effects on society, independent of its relation to individual income. For example, large differences in income can result in spatial concentrations of poverty, leading to diminished levels of social cohesion and social capital.
Acute myocardial infarction, heart failure, and pneumonia are among the most common causes of hospitalization among Medicare beneficiaries. In recent years, the outcomes associated with hospital care for these conditions have come under increasing scrutiny. Hospital outcomes are now made available to the public on government and privately run websites, and are the subject of pay for performance programs. Although many of the clinical factors associated with short term mortality and readmission have been defined, the effects of environmental factors—such as income distribution—on communities and individuals are poorly understood, and could help explain geographic variation in patient outcomes. We therefore examined the association between income inequality and risk of mortality and readmission among patients hospitalized for acute myocardial infarction, heart failure, and pneumonia. Using multilevel modeling techniques, we sought to distinguish contextual health effects of inequality from those effects of individual income and other factors.