1. Minister's Secretariat, Ministry of Health, Labour and Welfare A rapid rate of aging in urban areas http://www.mhlw.go.jp/stf/shingi/2r98520000032exf-att/2r98520000032f26.pdf
2. Homebound status and life space among Japanese community-dwelling elderly in an urban area;Murayama;Nihon Koshu Eisei Zasshi,2011