1. Department of Economics, Korea University, 5-1 Anam-Dong, Sungbuk-Ku, Seoul, 136-701, Korea, .
2. School of Economics and Business, Hoseo University, 268 Ansea-Dong, Cheonan, Chungnam, 330-180, shyoo @office. hoseo. ac.kr.
3. Department of Economics, Korea University, 5-1 Anam-Dong, Sungbuk-Ku, Seoul, 136-701, Korea, Korea, .