Quantitative measurements of inequality in geographic accessibility to pediatric care in Oita Prefecture, Japan: standardization with complete spatial randomness

Abstract

Background: A quantitative measurement of inequality in geographic accessibility to pediatric care as well as that of mean distance or travel time is very important for priority setting to ensure fair access to pediatric facilities. However, conventional techniques for measuring inequality is inappropriate in geographic settings. Since inequality measures of access distance or travel time is strongly influenced by the background geographic distribution patterns, they cannot be directly used for regional comparisons of geographic accessibility. The objective of this study is to resolve this issue by using a standardization approach.

Methods: Travel times to the nearest pediatric care were calculated for all children in Oita Prefecture, Japan. Relative mean differences were considered as the inequality measure for secondary medical service areas, and were standardized with an expected value estimated from a Monte Carlo simulation based on complete spatial randomness.

Results: The observed mean travel times in the area considered averaged 4.50 minutes, ranging from 1.83 to 7.02 minutes. The mean of the observed inequality measure was 1.1, ranging from 0.9 to 1.3. The expected values of the inequality measure varied according to the background geographic distribution pattern of children, which ranged from 0.3 to 0.7. After standardizing the observed inequality measure with the expected one, we found that the ranks of the inequality measure were reversed for the observed areas.

Conclusions: Using the indicator proposed in this paper, it is possible to compare the inequality in geographic accessibility among regions. Such a comparison may facilitate priority setting in health policy and planning.

Figure 1

Hypothetical examples of distribution patterns. For theoretical consideration, children (white circles) and pediatric facilities (black bullets) are supposed to be distributed differently: (a) regular, (b) clustered, and (c) circular arrangements. Each line connects a child to a pediatric facility.

Figure 2

Map of children and pediatric care facilities in Oita Prefecture. The distribution of child population is shown using a green proportional symbol, the area of which corresponds to the population. The location of the pediatric facilities is denoted as in blue. Brown and gray solid lines are used to denote the road network and the administrative boundaries, respectively. The small top-right window shows a map of Japan with the shaded region representing Oita Prefecture.

Figure 3

Shortest path from a child to the nearest pediatric facility. The shortest path from a child to the nearest pediatric facility is drawn with a brown solid line. The remaining symbols and lines are the same as in Figure 2.

Figure 4

Box plot of the travel time by secondary medical service area. The travel time (in minutes) of the shortest path by secondary medical service area is summarized. The box denotes the interquartile range, and the centerline of the box expresses the median. The extreme data points are shown when there exist outside whiskers that are 1.5 times longer than the interquartile range.