1. Department of Economics, University of Florida, Gainesville, Florida 32611;
2. Rimini Center for Economic Analysis, Italy;
3. Autoridade da Concorrência, Lisboa 1050-037, Portugal;
4. Business Research Unit, University Institute of Lisbon, Lisboa 1649-026, Portugal;
5. Formerly, Department of Economics, University of North Carolina at Chapel Hill;
6. FGV EPGE Brazilian School of Economics and Finance, Praia de Botafogo 190, Rio de Janeiro, RJ 22250, Brazil;
7. Amazon, Seattle, Washington 98109