1. Katsushi S. Imai (corresponding author), Department of Economics, School of Social Sciences, University of Manchester, Arthur Lewis Building, Oxford Road, Manchester M13 9PL, UK
2. Takahiro Sato, Research Institute for Economics & Business Administration (RIEB), Kobe University, 2-1 Rokkodai, Nada-ku, Kobe, Hyogo657-8501, Japan