Showing papers by "Roger A. Horn published in 1991"

The relationship between severity of illness and hospital length of stay and mortality.

Abstract: To address the question of quantification of severity of illness on a wide scale, the Computerized Severity Index (CSI) was developed by a research team at the Johns Hopkins University. This article describes an initial assessment of some aspects of the validity and reliability of the CSI on a sample of 2,378 patients within 27 high-volume DRGs from five teaching hospitals. The 27 DRGs predicted 27% of the variation in LOS, while DRGs adjusted for Admission CSI scores predicted 38% and DRGs adjusted for Maximum CSI scores throughout the hospital stay predicted 54% of this variation. Thus, the Maximum CSI score increased the predictability of DRGs by 100%. We explored the impact of including a 7-day cutoff criterion along with the Maximum CSI score similar to a criterion used in an alternative severity of illness measure. The DRG/Maximum CSI score's predictive power increased to 63% when the 7-day cutoff was added to the CSI definition. The Admission CSI score was used to predict in-hospital mortality and correlated R = 0.603 with mortality. The reliability of Admission and Maximum CSI data collection was high, with agreement of 95% and kappa statistics of 0.88 and 0.90, respectively.

Inequalities for unitarily invariant norms and bilinear matrix products

Abstract: We give several criteria that are equivalent to the basic singular value majorization inequality (1.1) that is common to both the usual and Hadamard products. We then use these criteria to give a unified proof of the basic majorization inequality for both products. Finally, we introduce natural generalizations of the usual and Hadamard products and show that although these generalizations do not satisfy the majorization inequality, they do satisfy an important weaker inequality that plays a role in establishing their submultiplicativity with respect to every unitarily invariant norm.

Linear operators preserving certain equivalence relations on matrices

Abstract: Using a uniform approach, characterizations are obtained of linear operators on matrix spaces that preserve certain equivalence relations such as consimilarity, $ * $-congruence, nonsingular equivalence, and unitary equivalence.

Classifying patients with burns for hospital reimbursement: diagnosis-related groups and modifications for severity.

Abstract: This study was designed to evaluate the relative severity and resource consumption of hospitalized patients with burns in a national cross section of hospitals, both with and without burn centers. We investigated to determine whether clinical variables or severity of illness measures not recorded in the Uniform Hospital Discharge Data Set are significant in explaining variation in length of stay, total cost, and mortality for patients with burns. The ability of the six burn diagnosis-related groups (DRGs) to explain variation in patients' length of stay was 20% and their ability to predict total costs was 24%. For the same patient population, the explanatory power of the DRGs improved to 54% for length of stay and 44% for costs when these variables were adjusted by the Severity of Illness Index. We also investigated whether hospitals with burn centers treated a more severely ill population of patients with burns than did hospitals without such centers. Significantly higher levels of severely ill patients with burns (p less than or equal to 0.0001) were found at burn center hospitals. Other patients or treatment variables, combined with a case-mix severity measure, were evaluated for their ability to further increase the explanatory power of DRGs. We also discuss here the use of the study results for reevaluating reimbursement policy.