1. Office of Institutional Research, Hokkaido University, Kita 8, Nishi 5, Kita-ku, Sapporo, Hokkaido 060-0808, Japan
2. Faculty of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo, Hokkaido 060-0814, Japan
3. National Institute of Technology, Kushiro College, 2-32-1 Otanoshike-Nishi, Kushiro 084-0916, Japan