1. Department of Economics, University of Oslo, Post Box 1095 Blindern, 0317 Oslo, Norway (email: )
2. Department of Economics, University of California, San Diego, 9500 Gilman Drive 0508, La Jolla, CA 92093 (email: )
3. Department of Economics, Norwegian School of Economics, Helleveien 30, 5045 Bergen, Norway (email: )
4. Department of Economics, University of Chicago, 1126 East 59th Street, Chicago, IL 60637 (email: )