First Author:   Akiko Sato Oishi Faculty of Law and Economics, Chiba University oishi@le.chiba-u.ac.jp   Chiba, 263-8522, Japan   +81-43-290-3579(Phone) +81-43-290-3579(Fax) Second Author: Yukiko Abe Graduate School of Economics and Business Administration, Hokkaido University abey@econ.hokudai.ac.jp   Kita 9, Nishi 7, Kita-ku Sapporo, 060-0809, Japan   +81-11-706-3860(Phone) +81-11-706-4947(Fax)