Correlations among risk-standardized mortality rates and among risk-standardized readmission rates within hospitals

Hospital-level, 30-day risk-standardized mortality and readmission rates are publicly reported for Medicare patients admitted with acute myocardial infarction (AMI), heart failure (HF), and pneumonia, but the correlations among mortality rates and among readmission rates within US hospitals for these conditions are unknown. Correlation among measures within the same hospital would suggest that there are common hospital-wide quality factors.

We designed a cross-sectional study of US hospital 30-day risk-standardized mortality and readmission rates for Medicare fee-for-service beneficiaries from July 2007 to June 2009. We assessed the correlation between pairs of risk-standardized mortality rates and pairs of risk-standardized readmission rates for AMI, HF, and pneumonia.

The mortality cohort included 4559 hospitals, and the readmission cohort included 4468 hospitals. Every mortality measure was significantly correlated with every other mortality measure (range of correlation coefficients, 0.27-0.41, P < 0.0001 for all correlations). Every readmission measure was significantly correlated with every other readmission measure (range of correlation coefficients, 0.32-0.47, P < 0.0001 for all correlations). For each condition pair and outcome, one-third or more of hospitals were in the same quartile of performance. Correlations were highest within large, nonprofit, urban, and/or Council of Teaching Hospitals members. For any given condition pair, the correlation between readmission rates was significantly higher than the correlation between mortality rates (P < 0.01 for all pairs).

Risk-standardized readmission rates are moderately correlated with each other within hospitals, as are risk-standardized mortality rates. This suggests that there may be common hospital-wide factors affecting hospital outcomes.