Abstract
IMPORTANCE: The 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. OBJECTIVE: To investigate the association between hospital-level physician proportion and 30-day risk standardized mortality rate (RSMRs) for six common inpatient conditions. DESIGN: Cross-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. SETTING: Nation-wide U.S. hospitals treating traditional Medicare beneficiaries in 2022. PARTICIPANTS: Medicare beneficiaries hospitalized for acute myocardial infarction, Chronic Obstructive Pulmonary Disease (COPD), Coronary Artery Bypass Graft (CABG) Surgery, heart failure, pneumonia, or stroke. EXPOSURES FOR OBSERVATIONAL STUDIES: Hospital-level physician proportion, defined as the number of physicians divided by the sum of affiliated physicians and APPs. MAIN OUTCOMES AND MEASURES: Hospital-level condition-specific 30-day RSMRs - case-mix adjusted outcome measures presented as proportions. RESULTS: Among 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 RELEVANCE: Higher 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.