Regional Correlation between Physician Supply and Hospital Discharges in Japan: A Cross-Sectional Comparative Analysis Using Nationwide Prefectural Data

Aim: This study aimed to evaluate regional equity in physician distribution across Japan by analyzing the correlation between physician supply and inpatient discharges in all 47 prefectures. The objective was to identify mismatches between workforce allocation and healthcare demand and to visualize disparities using a quadrant-based framework. Methods: We conducted a cross-sectional ecological analysis using publicly available 2021 data from the Ministry of Health, Labour and Welfare and the Statistics Bureau of Japan. The number of physicians and inpatient discharges per 100,000 population was calculated for each prefecture. Spearman’s rank correlation coefficients were used to assess the relationship between physician supply and hospitalization rates. Subgroup analysis by population size and a quadrant-based classification were applied to explore regional differences. Results: Descriptive statistics revealed notable regional variation: the mean physician supply was 250.3 per 100,000 population (SD = 40.6), and the mean discharge rate was 5,763.3 per 100,000 (SD = 689.4). While the overall correlation between physician density and discharge rates was weakly positive (ρ = 0.032), stratified analysis showed a strong negative correlation in highly populated prefectures (ρ = − 0.694, p  = 0.012). Quadrant analysis grouped prefectures into four categories based on median values, showing that underserved areas (low physician supply, high discharge rates) were predominantly rural, whereas metropolitan areas generally exhibited high physician supply and lower hospitalization rates. Conclusions: Despite Japan’s universal health coverage, considerable regional disparities persist in both physician distribution and healthcare utilization. The quadrant framework serves as a practical tool to identify critical mismatches between supply and demand. These findings emphasize the need for region-specific workforce strategies to promote equitable healthcare access. Trial registration Not applicable.