1. H. John Heinz III College; Carnegie Mellon University; Pittsburgh Pennsylvania 15213 U.S.A.
2. University of Bristol
3. National Bureau of Economic Research
4. Department of Policy Analysis and Management; Cornell University; 108 Martha Van Rensselaer Hall Ithaca New York 14853 U.S.A.
5. Department of Economics; Terry College; University of Georgia; 513 Brooks Hall Athens Georgia 30602 U.S.A.