The major independent variable was the team assignment of each admission (teaching hospitalist vs nonhospitalist). In addition, we examined patient- and physician-level covariates for each admission. Patient-level covariates included demographic characteristics (age, sex, and race or ethnicity), insurance status, number of prior admissions within the previous 90 days, albumin value at the time of admission, diagnosis of diabetes mellitus (defined as an ICD-9 code of 250 at discharge), DRG weight, primary discharge diagnosis (ICD-9 code), and discharge disposition (home with self-care, home with services, or nursing home). Because the source of data was a clinical information system, independent variables used for adjusted analyses could only be those available on most of the patients. We used DRG weight as a surrogate for the overall severity of illness, as has been done previously,14 because it was readily available on all patients. For length-of-stay analyses, we categorized DRG weight into quartiles, which represent levels of patient acuity. Albumin level at the time of admission was also used as a marker for overall disease severity, as has been done in earlier studies,20- 22 because it is available on most patients and is thought to be useful in the quantification of risk in research settings.23 The ICD-9 codes were grouped into diagnosis clusters using the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality system.24 Some of these diagnoses were further collapsed into clinical categories to make data reporting manageable (eg, neoplasm contains several Agency for Healthcare Research and Quality diagnosis classifications). For LOS analyses, only those diagnoses that were among the top 30 causes for hospitalization in the United States25 were included, to ensure adequate numbers of patients in each category. The major physician-level covariate of interest was the annual number of months on the service. There was no crossover of attending physicians between groups (ie, nonhospitalists never became hospitalists or vice versa).