A multi-modal relative spatial access assessment approach to measure spatial accessibility to primary care providers

Lin, Yan; Wan, Neng; Sheets, Sagert; Gong, Xi; Davies, Angela · 2018 · DOAJ

DOI: 10.1186/s12942-018-0153-9

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Summary

This paper addresses the limitations of the Enhanced Two-Step Floating Catchment Area (E2SFCA) method in measuring spatial accessibility to primary care providers. While multi-modal E2SFCA methods provide more realistic accessibility representations than single-mode approaches, they suffer from significant uncertainty due to the subjective choice of impedance coefficients in weighting functions, such as the Gaussian function. To resolve this, the authors propose a multi-modal relative spatial access assessment approach that incorporates the Spatial Access Ratio (SPAR). SPAR normalizes individual access scores by the mean access score of the study area, aiming to reduce variability caused by impedance coefficient selection. The study was conducted in the Albuquerque metropolitan area in New Mexico, USA, focusing on access to primary care physicians (PCPs). The researchers utilized data from the National Provider Identifier records, Infogroup, and the American Community Survey to identify 1,166 PCPs and estimate population subsets based on vehicle ownership. Transportation networks were modeled using ESRI StreetMap Premium for car travel and General Transit Specification Feed (GTFS) data for bus travel. The methodology involved three steps: calculating supply-to-demand ratios for each PCP location using mode-specific catchment sizes (30 minutes for cars, 60 minutes for buses); computing mode-specific and integrated Spatial Access Indices (SPAI); and finally, deriving SPAR values by dividing individual SPAI scores by the area’s average SPAI. Sensitivity analysis was performed to compare the stability of SPAI and SPAR across different impedance coefficients. The results demonstrated that traditional spatial access scores (SPAI) varied significantly when different impedance coefficients were applied, with statistical significance (p < 0.05). In contrast, the Spatial Access Ratio (SPAR) remained stable regardless of the impedance coefficient chosen (p = 1). This indicates that SPAR effectively mitigates the uncertainty inherent in the E2SFCA method’s weighting functions. The study confirms that while absolute access scores are sensitive to methodological parameters, relative access measures provide a robust and consistent assessment of spatial accessibility disparities. The significance of this research lies in its contribution to health geography and spatial analysis methodologies. By validating SPAR as a stable metric, the paper offers a reliable tool for policymakers and planners to assess equitable access to healthcare services without the confounding effects of arbitrary parameter choices. This approach allows for more accurate identification of underserved populations, particularly those reliant on public transportation, thereby supporting better-informed transportation planning and healthcare resource allocation. The findings underscore the importance of using relative rather than absolute measures in spatial accessibility studies to ensure reproducibility and comparability across different contexts.

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