Y. Zheng
Background: Hospital consolidation increasingly places multiple hospitals under common system control. However, spatial accessibility estimates alone do not indicate whether that accessibility is distributed across many health systems or concentrated within a few. Methods: We used the enhanced two-step floating catchment area (E2SFCA) method to estimate tract-level spatial accessibility to staffed beds at general hospitals reachable within 30 minutes by car. For tracts with positive E2SFCA scores, we aggregated hospital contributions by health system and calculated a Herfindahl-Hirschman Index (HHI) from each system's share of the tract's total E2SFCA score. We used Spearman rank correlations to examine associations with tract-level sociodemographic characteristics. Results: Of 163 reachable hospitals, 94 were outside New Jersey and accounted for 62.7% of staffed beds among these hospitals. Across 2,172 tracts, mean and median E2SFCA scores were 1.98 and 1.99 staffed hospital beds per 1,000 population, respectively. Among 2,161 tracts with positive E2SFCA scores, mean and median HHI values were 0.36 and 0.31. Using 2.0 for E2SFCA and 0.18 for HHI as descriptive reference values, 934 tracts had E2SFCA < 2.0 and HHI [≥] 0.18, while 655 had E2SFCA [≥] 2.0 and HHI [≥] 0.18. For seven of eight sociodemographic characteristics, correlations with E2SFCA and HHI were in opposite directions. Conclusions: Considering E2SFCA and HHI together provides a community-level view of spatial accessibility and how that accessibility is distributed across health systems. This framework may inform assessments of hospital consolidation and proposed service or capacity changes. Keywords: Spatial accessibility; hospital consolidation; E2SFCA; health systems; Herfindahl-Hirschman Index