1. Institute for Fiscal Studies, 7 Ridgmount Street, London WC1E7AE, United Kingdom, and University of Manchester (email: )
2. Institute of Fiscal Studies, 7 Ridgmount Street, London, WC1E7AE, and University College London (email: )
3. Institute of Fiscal Studies, 7 Ridgmount Street, London WC1E7AE, United Kingdom, and University College London (email: )
4. RAND Corporation, 1776 Main Street, PO Box 2138, Santa Monica, CA 90407 (email: )