There have been a number of literatures about the relationship between hospital volume and health outcomes. The previous literatures have indicated that for certain procedures and interventions, particularly complex surgery, there is a real possibility of improving outcomes by increasing activity volumes. The neurosurgery will be such a case. In the current study, we have investigated the relationship between volume and outcome (length of stay and charged cost) for surgical procedure of pituitary tumor. We have used the Japanese case-mix data, so called DPC from April 1, 2011 to March 31, 2012. There were 12,767 total discharge cases of pituitary tumor from 816 DPC hospitals. Among them we have used 2,664 surgical cases from 383 DPC hospitals. Using this dataset we have investigated the degree of concentration and factors associated with choice of procedures. Among the 383 facilities, all surgical cases were hypopituitarism or hyperpituitarism. Difference in sex was not clear and the age category 50-59 years old was the largest group. The upper 45 facilities treated 50% of surgical cases. For volume-outcome relationship, there were tendencies that higher case volume facilities had shorter ALOS (p=0.062, one-way analysis of variance) and smaller costs (p=0.087). Our result suggest the existence of volume-outcome relationship for pituitary surgery and the necessity of concentration of cases for better cost effectiveness.

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In order to extend the applied field of casemix based evaluation system to psychiatric care, the authors have analyzed the resource consumption of patients of whom main diagnosis was psychiatric disorders. The DPC data (April 1, 2011 to March 31, 2012) of 37,598 cases from 900 hospitals was used for the analysis. In order to focus on the acute cases, the analyzed cases were limited to those with 90 length of stay (LOS) and less. The differences in LOS were compared according to the ADL level at admission, GAF score at admission, sex, age category (15 years old and less, between 16 and 64, 65 years old and more) and experience of isolated hospitalization. The results have clarified that GAF score at admission, experiences of isolated hospitalization, 65 years old and more and specific care by psychiatrist. The above mentioned factors are not used for classification logic of the current DPC system. In order to expand the application area of DPC based patient grouping, it is recommended to elaborate the grouping logic according to the results of this study.

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Number of patients with mental disorders is increasing in Japan. According to the Patient survey of 2008, the patient of mental disorders has increased from 2,181 thousands of 1996 to 3,233 thousands of 2008. Reflecting this situation, it becomes an important issue how to properly treat the mental disorders among the in-patients of acute somatic care hospitals. In order to clarify the actual situation, we have investigated the prevalence of psychiatric problem as comorbidities and complications among 2,170,720 cases from 900 DPC hospitals from 1^st July to 31^st October 2010. In total, 144,342 of 2,170,720 cases (6.6%) had some kinds of mental disorders. The highest percentage was observed for MDC01 (17,893 of 142,426 cases: 12.6%) followed by MDC16 (17,357 of 153,743 cases: 11.3%) and MDC10 (7,862 of 71,227 cases: 11.0%) except for MDC17 (Psychiatric DPC group: 100.0%). The highest disorder was dementia (P0+P9=32,788+13,539=46,327), followed by F3 (Mood disorders), F4 (Neurotic, stress-related and somatoform disorders) and F2 (Schizophrenia, schizotypal and delusional disorders). The present study has indicated the needs of psychiatric care are large in the Japanese acute somatic care hospitals.

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Japan established an original case-mix classification system in 2002, so called Diagnosis Procedure Combination (DPC). The main purposes of introducing the DPC system are providing transparency of hospital performance as well as implementing an electronic billing system. Researchers can utilize the DPC data to identify, track, and analyze national trends in health care utilization, access, quality, outcomes, and costs. The unique advantage of the DPC data is the inclusion of detailed process data and several clinical data, which can be applied to academic studies on clinical epidemiology and health services research. The present report reviews the details of the DPC data in term of the structure of the DPC, the scale and contents of the DPC database, and the usability of the DPC data for clinical epidemiology and health services research as compared with the US Nationwide Inpatient Sample database.

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