1. Department of Economics, University College London, London, WC1 6BT, UK, and Centre for Economic Performance, London School of Economics, London, WC2A 2AE, UK.
2. Department of Economics, Helsinki School of Economics, 00101 Helsinki, Finland; Government Institute for Economic Research (VATT), 00101 Helsinki, Finland; and Department of Econonmics and Statistics, Åbo Akademi University, 20500 Turku, Finland.