1. Stockholm School of Economics, Sveavägen 65, 113 83 Stockholm, Sweden, and CEPR (e-mail: )
2. ICREA-MOVE, Universitat Autonòma de Barcelona, Edifici B, Campus de Bellaterra, Facultat d'Economia, 08193 Bellaterra, Spain, and Barcelona GSE (e-mail: )
3. Economics Department, Pennsylvania State University, 517 Kern Graduate Building, University Park, PA 16802, and NBER (e-mail: )