1. Robert H. Smith School of Business University of Maryland 7621 Mowatt Ln College Park MD20742USA
2. Graduate School of Business and Administration Hitotsubashi University 2‐1 Naka Kunitachi, Tokyo186‐8603Japan
3. Graduate School of Economics Hitotsubashi University 2‐1 Naka Kunitachi, Tokyo186‐8603Japan
4. Faculty of Commerce Waseda University 1‐6‐1 Nishiwaseda Shinjuku, Tokyo169‐8050Japan