Psychiatric standardized claim ratios by rurality and deprivation in Japan: A nationwide ecological study with contextual suicide mortality

Aim: We examined whether rurality was associated with psychiatric standardized claim ratios computed using medical-institution location, and how these patterns related to area deprivation and residence-based suicide mortality in Japan. Methods: We conducted a nationwide ecological study of 335 secondary medical areas. Rurality, measured with the Rurality Index for Japan, and a census-based Area Deprivation Index were population-weighted from municipalities. Psychiatric specialty therapy claims (April 2023 to March 2024) from Japan's national health-insurance claims open data were expressed as standardized claim ratios: observed claims billed by institutions in each area divided by national age-sex expected claims. Suicide deaths (April 2022 to March 2025) were expressed as age-sex standardized mortality ratios. Ecological rate-ratio trends were estimated with quasi-Poisson models. Results: Outpatient claim ratios were lower in rural than urban areas but non-monotonic (most urban, 108.4; fourth quintile, 76.9; and most rural, 81.3). Inpatient ratios peaked in the second quintile, and suicide mortality rose with rurality. Per 10-point higher rurality score, outpatient volume was lower (rate ratio, 0.939; 95% confidence interval, 0.921-0.956) and remained lower after including deprivation (0.919; 0.896-0.942); the rurality-suicide association attenuated. Nearest-three-area pooling raised the most rural median outpatient ratio from 62.2 to 101.1. Conclusion: More rural areas had lower outpatient psychiatric claim volume billed by local institutions relative to national age-sex benchmarks, but this contrast narrowed after nearest-area pooling, consistent with cross-boundary care. These institution-location ratios should prompt local review with residence-based and capacity data, not be read as evidence of under-provision.