1. Resources for the Future, Washington, DC 20036, USA.
2. Frank Batten School of Leadership and Public Policy, University of Virginia, Charlottesville, VA 22904, USA.
3. Regulatory Studies Center, The George Washington University, Washington, DC 20052, USA.
4. Brookings Institution, Washington, DC 20036, USA.
5. School of Public and Environmental Af airs, Indiana University, Bloomington, IN 47402, USA.
6. University of Wyoming, Laramie, WY 82071, USA.
7. Vanderbilt Law School, Vanderbilt University, Nashville, TN 37203, USA.