In 2004, Niigata University Hospital had 810 inpatient beds, 23 clinical departments and medical staff of 818. The service area of the hospital as a tertiary care hospital covers all districts in Niigata Prefecture, which has a population of 2,400,000. There are 34 paediatric inpatient beds in ward for children. These beds do not include beds for paediatric surgery patients. The size of the hospital is typical for a Japanese university hospital.
Patient data were analyzed for all children and adolescents under fifteen years of age who had received inpatient care at Niigata University Hospital during the period from April 2004 to March 2005. Information on paediatric inpatients under 15 years of age was collected. Data on patient age, sex, residential address, route of referral to Niigata University Hospital, discharge diagnosis classified by Japanese case mix classification for inpatients (diagnosis procedure combination, DPC) [5, 6], length of hospital stay (LOS), outcome of admission and route of referral from Niigata University Hospital were obtained from the hospital information system. In the DPC system, patient discharge is classified into 16 major diagnostic categories and 1,727 case-mix groups. Data on average and standard deviation (SD) of LOS of the patients in Japan, who were assigned to each DPC, were obtained from the Ministry of Health, Labour and Welfare. Data on age-structured population per district were obtained from National Census of Japan conducted by the Ministry of Internal Affairs and Communications in 2000.
Data on population per district were converted to data on population per 2 km mesh using the GIS software ArcView GIS 3.1a and ArcGIS 9 (Environment Systems Research Institute Inc., CA, USA). Data on locations of paediatric clinics and hospitals with paediatric wards were obtained from lists of the Japan Paediatric Association, Japanese Society of Paediatrics, Japan Medical Association and their local organizations. Road network data also contain codes for different classes of roads, average car speed and rules of the roads in order to calculate how long it would take to drive along a particular road segment .
Referral from clinics and other hospitals
To study the geographic distribution of patients admitted to Niigata University Hospital, empirical Bayesian estimates for the rate of inpatients per childhood population at risk were plotted on a GIS map with 2 km meshes . To study the relationship between spatial accessibility to Niigata University Hospital and the distribution of patients, the number of inpatients who lived within an area that is a certain time by car from Niigata University Hospital was calculated by using Network Analyst (ESRI Japan). The same procedure was performed for other hospitals in Niigata Prefecture in order to compare the inpatient service areas of Niigata University Hospital and general hospitals. The general hospitals had 177 to 312 inpatient beds and one or two paediatricians. Residence records for the patients admitted to the five hospitals in Niigata City were obtained from annual reports published by the hospitals. The distribution of patients referred from other medical facilities was plotted on GIS maps using the kernel density method [9, 10] and was compared with the distribution of paediatricians. For the kernel density method, we computed a density layer using a one-kilometre service area radius and a 200-meter-square area as a cell size, which yields a smooth map resolution. To differentiate the patients who have more complex conditions and those who have not, the patients were subdivided into two groups according to the information on DPC of each patient: one group of patients who had severe complications and one group of patients who did not have severe complications. The patients were also subdivided into those who admitted through emergency or taken to the hospital by ambulance and those who were not.
Referral to aftercare
For the purpose of this study, aftercare was defined as referral to a paediatric aftercare program, such as outpatient care and transfer to paediatric wards of other hospitals, not including foster care, a group home or a nursing home . Distributions of patients referred to the Outpatient Department of Niigata University Hospital, patients referred to outpatient care of other medical facilities and patients transferred to paediatric wards of other hospitals were plotted on GIS maps. Since delay in referral of a patient to aftercare prolongs LOS of the patient, spatial differences in LOS of inpatients might reflect the spatial differences in accessibility to aftercare. To estimate the spatial differences in accessibility to aftercare, LOS of each patient was scored and plotted on a GIS map. The SD scores for LOS (LOSSDS) of a patient who was assigned to a DPC were calculated as follows:
Contour maps of LOSSDS of the patients were produced by interpolation using the ordinary Kringing method .