Comparing alternative methods of measuring geographic access to health services

Objective: This research compared alternative measures of geographic access to health care providers using different levels of spatial aggregation (county, zipcode and street) and different methods of calculating the cost of space (Euclidean distance, road distance and travel time). Data Sources: The research is based on a community-based sample of rural (74%) and urban (26%) Arkansans (n = 435) and all medical providers (n = 3, 419) and mental health specialists (n = 1, 034) practicing in the state of Arkansas in 1993. Study Design: A cross-sectional study design was used to determine the availability of and accessibility to general medical and specialty mental health providers. Accessibility was defined as the travel time between each subject and the closest provider. Availability was defined as the number of providers within 30 minutes travel time of each subject. Data Collection: A Geographic Information System was used to geocode subjects and providers at the county, zip code and street levels, and to calculate the travel times, road distances and Euclidean distances between subjects and providers. Principal Findings: Regression results demonstrated that the most commonly used county-based measures of geographic access (e.g., MSA designation and providers per capita) explained 3%-10% of the variation in accessibility and 34%-70% of the variation in availability. Conclusions: Results indicate that Geographic Information Systems can be used to accurately measure geographic access to health services in a cost effective manner.