Area-Level Correlates of Inpatient Care Self-Sufficiency in Subnational Health Planning Areas: A Disease-Stratified Ecological Study from Aichi Prefecture, Japan

Background/Objectives: Japan organizes inpatient care through secondary medical areas (SMAs), but evidence linking area-level care self-sufficiency with population need, healthcare supply, and socioeconomic context is limited. We quantified disease-stratified self-sufficiency across Aichi Prefecture and examined its ecological correlates. Methods: This cross-sectional ecological study analyzed fiscal-year 2024 Diagnosis Procedure Combination discharges from 203 of 276 acute-care hospitals across 11 SMAs. The dataset comprised 396 cells (11 SMAs × 18 Major Diagnostic Categories × surgical/non-surgical strata) linked to census, healthcare-resource, household, and pooled 2020–2024 standardized mortality ratio (SMR) data. Pre-specified single-predictor regressions at the SMA level (n = 11) were supplemented by spatial and cluster-robust sensitivity analyses. Self-sufficiency represented observed resident-to-provider flows within the participating hospital network. Results: Mean self-sufficiency ranged from 34.0% to 88.3% across SMAs (intra-class correlation, 0.54) and was 8.5 percentage points lower for surgical cells (95% CI, 5.9–11.1). Greater shares of residents aged ≥75 years (β = −12.80; 95% CI, −22.84 to −2.75) and households containing an elderly member (β = −13.53; 95% CI, −23.02 to −4.05) were the strongest negative correlates. Supply-density estimates were consistently positive; in the cell-level sensitivity model, physician, general-bed, and psychiatric-bed densities were associated with above-median self-sufficiency (ORs, 2.51–3.16). Exploratory analyses suggested differing patterns across acute and chronic conditions. Conclusions: Self-sufficiency varied substantially across planning areas and was associated with demographic, household, supply, and mortality characteristics. These findings support disease-specific evaluation of regional concentration versus local completion but do not establish causal or individual-level relationships. Multi-prefecture studies with individual-level case-mix adjustment are needed before resource-allocation applications.