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Income inequality and 30 day outcomes after acute myocardial infarction, heart failure, and pneumonia: retrospective cohort study

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f521 (Published 14 February 2013) Cite this as: BMJ 2013;346:f521
  1. Peter K Lindenauer, associate professor of medicine123,
  2. Tara Lagu, assistant professor of medicine123,
  3. Michael B Rothberg, associate professor of medicine123,
  4. Jill Avrunin, statistician1,
  5. Penelope S Pekow, senior statistician14,
  6. Yongfei Wang, lecturer in medicine, senior statistician56,
  7. Harlan M Krumholz, Harold J Hines Jr professor of medicine567
  1. 1Center for Quality of Care Research, Baystate Medical Center, Springfield, MA 01199, USA
  2. 2Division of General Internal Medicine, Baystate Medical Center, Springfield, MA, USA
  3. 3Department of Medicine, Tufts University School of Medicine, Boston, MA, USA
  4. 4Division of Biostatistics and Epidemiology, Department of Public Health, University of Massachusetts-Amherst, Amherst, MA, USA
  5. 5Center for Outcomes Research and Evaluation, Yale-New Haven Hospital, New Haven, CT, USA
  6. 6Section of Cardiovascular Medicine and the Robert Wood Johnson Clinical Scholars Program, Department of Medicine, Yale School of Medicine, Yale University, New Haven, CT, USA
  7. 7Section of Health Policy and Administration, Yale School of Public Health, Yale University, New Haven, CT, USA
  1. Correspondence to: P K Lindenauer peter.lindenauer{at}bhs.org
  • Accepted 11 December 2012

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.

Footnotes

  • Contributors: PKL devised the study concept and design; analyzed, and interpreted the data; drafted the paper; and supervised the study. He is the guarantor. TCL, MBR, JSA, PSP, YW, and HMK analyzed and interpreted the data and critically revised the paper. HMK acquired the data and obtained funding. PKL had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

  • Funding: HMK is supported by grant U01 HL105270-02 (Center for Cardiovascular Outcomes Research at Yale University) from the National Heart, Lung, and Blood Institute.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: support from the National Heart, Lung, and Blood Institute for the submitted work; PKL, TCL, MBR, JSA, and PSP have no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; HMK is the recipient of a research grant from Medtronic, through Yale University and is chair of a cardiac scientific advisory board for UnitedHealth; PKL, TCL, MBR, JA, PSP, and YW have no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The institutional review board at Yale University approved the protocol.

  • Data sharing: No additional data available.

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