1. University of California at Berkeley, Goldman School of Public Policy, 345 GSPP, 2607 Hearst Avenue, Berkeley, CA 94720, and National Bureau of Economic Research (NBER) (e-mail: )
2. University of California at Davis, Economics Department, 1151 SSH, One Shields Avenue, Davis, CA, 95616, and NBER (e-mail: )
3. University of Connecticut, Economics Department, 344 Oak Hall, 365 Fairfield Way, Storrs, CT 06268 (e-mail: ).