Do severity measures explain differences in length of hospital stay? The case of hip fracture.

To examine whether judgments about hospital length of stay (LOS) vary depending on the measure used to adjust for severity differences. Data on admissions to 80 hospitals nationwide in the 1992 MedisGroups Comparative Database. For each of 14 severity measures, LOS was regressed on patient age/sex, DRG, and severity score. Regressions were performed on trimmed and untrimmed data. R-squared was used to evaluate model performance. For each severity measure for each hospital, we calculated the expected LOS and the z-score, a measure of the deviation of observed from expected LOS. We ranked hospitals by z-scores. All patients admitted for initial surgical repair of a hip fracture, defined by DRG, diagnosis, and procedure codes. The 5,664 patients had a mean (s.d.) LOS of 11.9 (8.9) days. Cross-validated R-squared values from the multivariable regressions (trimmed data) ranged from 0.041 (Comorbidity Index) to 0.165 (APR-DRGs). Using untrimmed data, observed average LOS for hospitals ranged from 7.6 to 23.9 days. The 14 severity measures showed excellent agreement in ranking hospitals based on z-scores. No severity measure explained the differences between hospitals with the shortest and longest LOS. Hospitals differed widely in their mean LOS for hip fracture patients, and severity adjustment did little to explain these differences.