1. Stanford Institute for Economic Policy Research (SIEPR), Stanford, CA 94305.
2. Stanford University Department of Economics, Economics Building, 247 Stanford, California 94305.
3. National Bureau of Economic Research, 1050 Massachusetts Avenue, Cambridge, MA 02138.
4. University of California, Berkeley, Department of Economics, 508-1 Evans Hall, Berkeley, CA 94720.
5. MIT Department of Economics, 50 Memorial Drive, Building E52, Room 350, Cambridge MA 02142.
6. MIT Department of Economics, 50 Memorial Drive, Building E52, Cambridge MA 02142.