Physician Workforce and Population Mortality: A Globally Validated Age-Structured Modeling Approach

BackgroundEvaluating long-term health workforce planning requires robust and globally valid indicators. While many existing metrics, such as patient satisfaction or healthcare utilization, are inherently uncertain over long horizons, mortality is an objective and stable metric. To analyze how physician supply impacts population health, we propose a model that links physician density to age-specific mortality rates and incorporate it to the age-sturctured dynamics. MethodsWe developed a unified model that links physician workforce density to age-structured mortality rates. Subsequently, we applied this model within a Lotka-McKendrick framework to simulate physician supply expansion scenarios in South Korea. The system simulates future age-specific mortality outcomes under varying physician supply scenarios, including a baseline intake of 3,058 physicians per year and an expanded intake of up to 7,058 physicians per year, projected through 2065. FindingsOur model was validated using WHO mortality data including Japan, the United States, and the United Kingdom. Its validity of our model holds across all age groups in each country, as confirmed by statistical analysis with false discovery rate correction (maximum adjusted p < 0.05). Using the age-structured dynamics with the model in South Korea, we confirm that future physician density increases even under the baseline scenario (3,058 physicians per year), and that projected population sizes under the baseline and the aggressive expansion scenario (7,058 physicians per year) are not statistically different (p > 0.07). Moreover, under the aggressive expansion scenario, the projected reductions in age-specific mortality rates by 2065 remain marginal: less than 0.27% for those under 65, less than 0.69% for ages 65-75, less than 2.75% for ages 75-84, less than 7.31% for ages 85-94, and less than 12.6% for ages 95-99. InterpretationIn well-resourced health systems facing aging populations and persistently low fertility rates, further expansion of physician supply alone offers limited mortality benefits. Our findings suggest a paradigm shift: from quantity-driven to efficiency-focused workforce strategies. The proposed method is readily adaptable to other contries, offering a policy-relevant and outcome-oriented tool for long-term health workforce planning. FundingNone. The funder had no role in study design, data collection, data analysis, data interpretation, or writing of the report. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSWe searched PubMed, Web of Science, and Google Scholar for studies published between 2000 and 2024 using terms such as "physician workforce," "healthcare workforce planning," "medical workforce density," and "age-structured dynamics." Most physician workforce planning models are either utilization-based (projected service demand) or needs-based (estimated population health requirements). These models often extrapolate current health service utilization rates or population health needs into the future, typically assuming that such values remain constant over time, despite the acknowledged difficulty of forecasting long-term demand dynamics. Additionally, methodologies differ widely across countries, which hampers direct comparisons of outcomes. Some metrics, such as patient needs or preferences, are also subjective and difficult to measure consistently. In contrast, more objective indicators like mortality rates are more readily available and comparable across settings. As far as we are aware, no published model has dynamically integrated physician density--endogenously derived from workforce supply--into an age-structured framework for projecting population mortality. Added value of this studyTo the best of our knowledge, this study is the first to integrate a model linking physician workforce density with age-structured mortality rates into the Lotka-McKendrick framework, capturing the interaction between physicians and populations across age groups. By modeling how changes in doctor-to-population ratios affect mortality, our approach moves beyond traditional models that treat health outcomes as exogenous. This allows novel analyses of policy scenarios, such as estimating life expectancy gains from increasing physician supply. Our model provides a unified framework to project both physician workforce dynamics and population health outcomes simultaneously. Implications of all available evidenceOur findings underscore the importance of explicitly linking age-structured population dynamics with physician density and mortality outcomes. Traditional models often overlook these interdependencies, risking inaccurate forecasts and limiting the relevance of cross-national comparisons. By capturing how physician supply influences mortality across age groups, our approach enables more precise, outcome-driven workforce planning.