First Author:   Toshihiro Matsumura Institute of Social Science, University of Tokyo matsumur@iss.u-tokyo.ac.jp   Institute of Social Science, University of Tokyo, 7-3-1, Hongo Bunkyo-ku, 113--0053, Japan   81-3-5841-4932(Phone) 81-3-5841-4932(Fax) Second Author: Takeshi Ebina Department of Social Engineering, Tokyo Institute of Technology ebina-t@soc.titech.ac.jp   2-12-1 Oh-okayama, Meguro-ku, Tokyo, 152-8552, Japan   (81)-3-5734-2929(Phone) (81)-3-5734-3622(Fax) Third Author: Daisuke Shimizu Faculty of Economics, Gakushuin University daisuke.shimizu@gakushuin.ac.jp   1-5-1, Mejiro, Toshima-ku, Tokyo, 171-8588, Japan   (81)-3-5992-3633(Phone)