Health, 2016, 8, 505-517 Published Online April 2016 in SciRes. http://www.scirp.org/journal/health http://dx.doi.org/10.4236/health.2016.86054 How to cite this paper: Nawata, K. and Kawabuchi, K. (2016) Did the Revision of the Japanese Medical Payment System Work Properly?—An Analysis of Averages and Variances of Length of Hospital Stay for Type 2 Diabetes Patients by Individ- ual Hospital. Health, 8, 505-517. http://dx.doi.org/10.4236/health.2016.86054 Did the Revision of the Japanese Medical Payment System Work Properly?— An Analysis of Averages and Variances of Length of Hospital Stay for Type 2 Diabetes Patients by Individual Hospital Kazumitsu Nawata 1 , Koichi Kawabuchi 2 1 Graduate School of Engineering, University of Tokyo, Tokyo, Japan 2 Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan Received 11 February 2016; accepted 8 April 2016; published 11 April 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract We evaluated the effects of the 2010 revision of the medical payment system on the length of stay (LOS). In this analysis, we assessed not only the average length of stay (ALOS), but also variance of LOS at individual hospitals. We used a dataset of 18,641 type 2 diabetes patients collected from 51 general hospitals. The variables found to affect LOS were age, comorbidities, complications, acute hospitalization, introduced by other hospitals, winter, one-week hospitalization, specific hospita- lization period, and principal diseases coded E11.5, E11.6 and E11.7. Although the effect was mar- ginal, the 2010 revision did reduce ALOS, and the reduction was larger as ALOS became longer. On the other hand, we did not find that the variance of LOS within hospitals became smaller. The re- sults of the study suggest that new incentives and assistance to hospitals to help them make effi- cient use of medical information are needed. Keywords Type 2 Diabetes, Length of Hospital Stay, Analysis of Variances 1. Introduction In June 2015, the advisory committee of the Ministry of Health, Labour and Welfare [1] submitted the very im-