1. William Barton Rogers Professor of Energy Economics, Sloan School of Management, Department of Applied Economics, Massachusetts Institute of Technology (MIT), 100 Main St., Cambridge, MA 02142, Director of the Center for Energy and Environmental Policy Research, and National Bureau of Economic Research (NBER) (e-mail: )
2. Bank of Tokyo-Mitsubishi Professor of Economics and Finance, Department of Applied Economics, Sloan School of Management, MIT, 100 Main St., Cambridge, MA 02142, and NBER (e-mail: )