First Author:   Wen-chung Guo Department of Economics, National Taipei University guowc@ntu.edu.tw   151, University Rd., San Shia, Taipei, 23741, Taiwan   +886-2-86741111#67156(Phone) +886-2-86741111#67156(Fax) Second Author: Ying-huei Chen Department of Economics, National Taipei University smilesun36@msn.com