First Author:   Noritaka Kudoh Hokkaido University kudoh@econ.hokudai.ac.jp   Department of Economics, Hokkaido University, Kita 9 Nishi 7, Kita-ku Sapporo, 060-0809, Japan       http://www.econ.hokudai.ac.jp/~kudoh/ Second Author: Hong Thang Nguyen Hokkaido University thangnh@econ.hokudai.ac.jp   Department of Economics, Hokkaido University, Kita 9 Nishi 7, Kita-ku Sapporo, 060-0809, Japan