Distance and the utilization of health facilities in rural Nigeria.

Inequalities in geographic access to health care result from the configuration of facilities, population distribution, and the transportation infrastructure. In recent accessibility studies, the traditional distance measure (Euclidean) has been replaced with more plausible measures such as travel distance or time. Both network and raster-based methods are often utilized for estimating travel time in a Geographic Information System. Therefore, exploring the differences in the underlying data models and associated methods and their impact on geographic accessibility estimates is warranted. We examine the assumptions present in population-based travel time models. Conceptual and practical differences between raster and network data models are reviewed, along with methodological implications for service area estimates. Our case study investigates Limited Access Areas defined by Michigan’s Certificate of Need (CON) Program. Geographic accessibility is calculated by identifying the number of people residing more than 30 minutes from an acute care hospital. Both network and raster-based methods are implemented and their results are compared. We also examine sensitivity to changes in travel speed settings and population assignment. In both methods, the areas identified as having limited accessibility were similar in their location, configuration, and shape. However, the number of people identified as having limited accessibility varied substantially between methods. Over all permutations, the raster-based method identified more area and people with limited accessibility. The raster-based method was more sensitive to travel speed settings, while the network-based method was more sensitive to the specific population assignment method employed in Michigan. Differences between the underlying data models help to explain the variation in results between raster and network-based methods. Considering that the choice of data model/method may substantially alter the outcomes of a geographic accessibility analysis, we advise researchers to use caution in model selection. For policy, we recommend that Michigan adopt the network-based method or reevaluate the travel speed assignment rule in the raster-based method. Additionally, we recommend that the state revisit the population assignment method.

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Measuring geographic access to health care: raster and network-based methods

Physician accessibility: an urban case study of pediatric providers

The willingness of patients in the rural tropics to seek medical care at primary health care facilities is influenced by the distance they must travel to receive that care. Distance decay effects in attendance rates were estimated from a database of 4348 attendances at a rural health center in the Wosera subdistrict of Papua New Guinea linked to demographic and house position data for the catchment population. Small-scale spatial patterns and differences between diagnoses age groups and gender are described. Men attended 15.3% more often than females. Attendance also varied by age and was highest among infants under 1 year old and adults aged 40 years and older. Attendance decreased considerably with distance with distance decay accounting for a 50% decrease in mean attendance at a distance of 3.5 km. This distance effect did not vary significantly among age groups or sexes but the effects are directly influenced by gender in different age groups being most pronounced among adolescents. Differences between major diagnosis groups time effects and the spatial heterogeneity of attendance are discussed.

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The effect of distance from home on attendance at a small rural health centre in Papua New Guinea

This paper demonstrates a method for estimating the geographical accessibility of public hospitals. Cost path analysis was used to determine the minimum travel time and distance to the closest hospital via a road network. This analysis was applied to 38,000 census enumeration district centroids in New Zealand allowing geographical access to be linked to local populations. Average time and distance statistics have been calculated for local populations by modeling the total travel of a population if everybody visited a hospital once. These types of statistics can be generated for different population groups and enable comparisons to be made between regions. This study has shown that the northern and southern parts of New Zealand have high average travel times to hospital services.

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Modeling population access to New Zealand public hospitals

Time and distance, the two common measures of travel, are examined as they relate to the use of various types of medical service facilities, using correlation and regression analysis. Different conclusions about the relative accessibility of health care facilities for selected sub-population groups result from the use of each measure separately. Differences in travel patterns to hospitals and those to physicians and dentists are observed when measured by time alone or by linear distance alone. Methodologic and health care implications are discussed.

G. W. Shannon

Papers

Time and distance: the journey for medical care.