Estimating spatially varying distance decay parameters in health care spatial accessibility studies

Authors: Kevin Matthews*, Centers for Disease Control and Prevention
Topics: Medical and Health Geography, Spatial Analysis & Modeling, Applied Geography
Keywords: colonoscopy, distance decay, 2SFCA, accessibility, health services
Session Type: Paper
Day: 4/5/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Marshall South, Marriott, Mezzanine Level
Presentation File: No File Uploaded


The likelihood of using a healthcare service decreases as the distance from a set of population (demand) locations to a set of provider (supply) locations increases. However, most spatial accessibility researchers include a single—global—distance decay parameter for an entire study area and are based on distances to nearest providers. We argue that a single parameter will lead to underestimated spatial accessibility measures in rural areas and overestimated measures in urban areas because the distances people need to travel to health care are naturally longer for rural populations than urban populations. Likewise, we argue that a distance decay parameter based on distances to the nearest providers will lead to underestimated spatial accessibility measures given that people frequently bypass their nearest providers. These biases can be minimized by estimating local distance decay parameters based on distances to chosen health care providers. We developed a spatial kernel regression method to estimate these local distance decay parameters. We used colonoscopy utilization data among Medicare beneficiaries in Ohio and the two-step floating catchment area (2SFCA) method to test the effects that spatially varying distance decay parameters have on measures of spatial accessibility. We show that global versus local distance decay parameters based on distances from the nearest versus chosen providers are significantly different. This case study provides an illustration for one method of computing spatially-varying distance decay parameters based on travel times to chosen providers. This approach has the potential to improve on the reliability of contemporary spatial accessibility measures.

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