First Author:   Megumi Mochida Graduate School of Economics, Osaka University@ cg088mm@srv.econ.osaka-u.ac.jp   Machikaneyama 1-7, Toyonaka, Osaka 560-43, Japan@@ Toyonaka, 560-0043, Japan   +81-6-6850-6111(Phone) +81-6-6850-6111(Fax)