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Article
January 12, 1990

The Importance of Severity of Illness in Assessing Hospital Mortality

Author Affiliations

From the Department of Health Policy Research, New York (NY) University Medical Center/New York University School of Medicine (Drs Green and Wintfeld); the Center for Hospital Finance and Management, The Johns Hopkins University, and the Department of Information Systems and Decision Sciences, Loyola College, Baltimore, Md (Dr Sharkey); and the Department of Medicine, UCLA Medical Center, Los Angeles, Calif (Dr Passman).

From the Department of Health Policy Research, New York (NY) University Medical Center/New York University School of Medicine (Drs Green and Wintfeld); the Center for Hospital Finance and Management, The Johns Hopkins University, and the Department of Information Systems and Decision Sciences, Loyola College, Baltimore, Md (Dr Sharkey); and the Department of Medicine, UCLA Medical Center, Los Angeles, Calif (Dr Passman).

JAMA. 1990;263(2):241-246. doi:10.1001/jama.1990.03440020075036
Abstract

Each year, the Health Care Financing Administration (HCFA) releases a report comparing hospital mortality rates with predicted rates. Some argue that the HCFA's prediction model does not adequately account for patient severity. We tested this hypothesis by comparing the HCFA's model (replicated as closely as we could) to a second that added a severity measure (the Stage of Principal Diagnosis at Admission, a subscale of the Severity of Illness Index). In our simulation, the HCFA's model had very limited capacity to predict mortality (average R2, 2.5%). Patients grouped according to admission severity had markedly different mortality rates, which the HCFA's model's predictions could not differentiate. The HCFA model also failed to predict large differences in mortality between hospitals with low- and high-severity admissions. Adding severity to the HCFA's model yielded more than an eightfold increase in the R2, to 21.5%, and reduced instances of higher than expected hospital mortality to chance levels. These findings suggest that the HCFA's mortality release needs to be made much more sensitive to admission severity before it can be used to make valid inferences about the quality or effectiveness of hospital care.

(JAMA. 1990;263:241-246)

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