1. Annual report on the aging society: 2014 http://www8.cao.go.jp/kourei/whitepaper/w-2014/gaiyou/s1_1.html
2. Population and social security surveys: January 2014 http://www.ipss.go.jp/syoushika/tohkei/newest04/h1_1.html
3. Patient survey: 2005 http://www.e-stat.go.jp/SG1/estat/List.do?lid=000001047097
4. Patient survey: 2011 http://www.e-stat.go.jp/SG1/estat/List.do?lid=000001103073
5. Survey of health and welfare trends: 2003 http://www.e-stat.go.jp/SG1/estat/GL08020103.do?_toGL08020103_&listID=000001054987&requestSender=dsearch