Primary care physician workforce and Medicare beneficiaries' health outcomes.

CONTEXT Despite a widespread interest in increasing the numbers of primary care physicians to improve care and to moderate costs, the relationship of the primary care physician workforce to patient-level outcomes remains poorly understood. OBJECTIVE To measure the association between the adult primary care physician workforce and individual patient outcomes. DESIGN, SETTING, AND PARTICIPANTS A cross-sectional analysis of the outcomes of a 2007 20% sample of fee-for-service Medicare beneficiaries aged 65 years or older (N = 5,132,936), which used 2 measures of adult primary care physicians (general internists and family physicians) across Primary Care Service Areas (N = 6542): (1) American Medical Association (AMA) Masterfile nonfederal, office-based physicians per total population and (2) office-based primary care clinical full-time equivalents (FTEs) per Medicare beneficiary derived from Medicare claims. MAIN OUTCOME MEASURES Annual individual-level outcomes (mortality, ambulatory care sensitive condition [ACSC] hospitalizations, and Medicare program spending), adjusted for individual patient characteristics and geographic area variables. RESULTS Marked variation was observed in the primary care physician workforce across areas, but low correlation was observed between the 2 primary care workforce measures (Spearman r = 0.056; P < .001). Compared with areas with the lowest quintile of primary care physician measure using AMA Masterfile counts, beneficiaries in the highest quintile had fewer ACSC hospitalizations (74.90 vs 79.61 per 1000 beneficiaries; relative rate [RR], 0.94; 95% confidence interval [CI], 0.93-0.95), lower mortality (5.38 vs 5.47 per 100 beneficiaries; RR, 0.98; 95% CI, 0.97-0.997), and no significant difference in total Medicare spending ($8722 vs $8765 per beneficiary; RR, 1.00; 95% CI, 0.99-1.00). Beneficiaries residing in areas with the highest quintile of primary care clinician FTEs compared with those in the lowest quintile had lower mortality (5.19 vs 5.49 per 100 beneficiaries; RR, 0.95; 95% CI, 0.93-0.96), fewer ACSC hospitalizations (72.53 vs 79.48 per 1000 beneficiaries; RR, 0.91; 95% CI, 0.90-0.92), and higher overall Medicare spending ($8857 vs $8769 per beneficiary; RR, 1.01; 95% CI, 1.004-1.02). CONCLUSION A higher level of primary care physician workforce, particularly with an FTE measure that may more accurately reflect ambulatory primary care, was generally associated with favorable patient outcomes.