Effect of distance and population size on patient trips in a prefecture of Japan: Application of a transportation distribution model to the demand for and supply of health services

The gravity model, a method for analyzing transportation distribution in transportation engineering, was used to explain patient trips between ten health service regions in a Japanese prefecture. The OD (Origin-Destination) tables were constructed with zoning by regions, distinguishing between out- and inpatients. The observed trips were determined from the data of a survey conducted in 1992 that reported the locations of patient residences and chosen medical facilities. The base values used in the model calculations were the population size of each region and the road distance between the centers of regions. Problems of intrazonal trip were avoided by setting a mean intrazonal movement distance. This model was calibrated by the linear regression method with simultaneous validation by the index of correlation coefficients. The model was found to accurately simulate the effect of distance on the choice of medical facilities and the differences between the characteristics of in- and out-patients. The population value in use showed the relation not only with demand but also the supply of clinical services. It was suggested that the model presented here was useful in the allocation of medical resources and would help explain the relationship between suppliers and consumers of medical services.