1. The Cabinet Office, Government of Japan: White Paper on Aging Society 2007 Edition, Ch. 3. Tokyo Office of Government Public Relations (2007) (in Japanese)
2. Yamaguchi, T., Sasama, R., Yamada, K.: Design and Concept of Network Robots as Social Agents to Motivate Elderly People. In: Proceedings of the IEEE/RSJ IROS 2009 Workshop (2009)
3. Levinger, G., Snoek, D.J.: Attraction in relationship: A new look at interpersonal attraction. General Learning Press (1972)
4. Fogg, B.J.: Persuasive Technology, pp. 64–66. Elsevier, Amsterdam (2003)
5. Nielsen//NetRatings: Transition of Composition ratio of Web User in the Age Bracket (2006),
http://csp.netratings.co.jp/nnr/PDF/Newsrelease11072006_J.pdf
(in Japanese)