1. University of Oslo, PO Box 95 Blindern, 0317 Oslo, Norway, ESOP, and CEP (e-mail: )
2. University of Oslo, PO Box 95 Blindern, 0317 Oslo, Norway, CEPR, and NBER (e-mail: )
3. University of Oslo, PO Box 95 Blindern, 0317 Oslo, Norway, ESOP, and CEPR (e-mail: )