1. Department of Economics, Copenhagen Business School, Porcelænshaven 16A, 1, DK2000 Frederiksberg, Denmark, and CBER.
2. Development Economics Group, Wageningen University, and Department of Economics, Tilburg University, Hollandseweg 1, 6700 EW, Wageningen, Netherlands.
3. Rady School of Management, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093.
4. Department of Economics, University of Chicago, 1126 E. 59th St., Chicago, IL 60637, and NBER.