Physician Composition of Hospitals' Workforce And Mortality Across U.S. Hospitals

ImportanceThe clinical workforce composition in U.S. hospitals is shifting, with advanced practice practitioners (APPs) - nurse practitioners and physician assistants -assuming larger roles in inpatient care. How this mix relates to patient mortality is unclear. ObjectiveTo investigate the association between hospital-level physician proportion and 30-day risk standardized mortality rate (RSMRs) for six common inpatient conditions. DesignCross-sectional national study linking 2022 CMS Physician & Other Practitioners, Facility Affiliation, Hospital Compare Complications and Deaths, and American Hospital Association Annual Survey data. Analyses were completed October 17, 2025. SettingNation-wide U.S. hospitals treating traditional Medicare beneficiaries in 2022. ParticipantsMedicare beneficiaries hospitalized for acute myocardial infarction, Chronic Obstructive Pulmonary Disease (COPD), Coronary Artery Bypass Graft (CABG) Surgery, heart failure, pneumonia, or stroke. Exposure(s) (for observational studies)Hospital-level physician proportion, defined as the number of physicians divided by the sum of affiliated physicians and APPs. Main Outcome(s) and Measure(s)Hospital-level condition-specific 30-day RSMRs - case-mix adjusted outcome measures presented as proportions. ResultsAmong 3,487 hospitals (mean physician proportion 79.7% [SD, 9.4%]), mean physician proportions across quartiles ranged from 67.8% (Q1; n=872; range, 25.0-73.5%) to 91.6% (Q4; n=871; range, 86.7-99.6%). Mean hospital-level RSMRs (%, 95% CI) were 12.63 (12.57-12.69) for acute myocardial infarction, 2.93 (2.88-2.99) for CABG surgery, 9.50 (9.44-9.56) for COPD, 12.03 (11.96-12.11) for heart failure, 18.12 (18.02-18.21) for pneumonia, and 13.74 (13.66-13.82) for stroke. Hospitals in the highest physician proportion quartile (Q4) had lower RSMRs than hospitals [p value, 95% CI] in the lowest quartile (Q1) for all conditions - acute myocardial infarction (12.54 vs. 12.86 [p<0.001, 0.16-0.48]), CABG (2.92 vs. 3.05 [p=0.106, -0.29-0.30]), COPD (9.11 vs. 9.83 [p<0.001, 0.56-0.88]), heart failure (11.24 vs. 12.73 [p<0.001, 1.29-1.70]), pneumonia (17.51 vs. 18.64 [p<0.001, 0.87-1.39]), and stroke (13.41 vs. 14.31 [p<0.001, 0.67-1.12]). Generalized additive models identified significant non-linear associations between the physician proportion and the RSMRs for COPD, acute myocardial infarction, heart failure, pneumonia, and stroke, respectively explaining 4.77-11.82% of the deviance. Conclusions and RelevanceHigher relative physician staffing was modestly but consistently associated with lower hospital-level mortality across common and high-burden medical conditions. Workforce composition may be a key structural determinant of hospital quality and warrants consideration in workforce and quality improvement strategies.