1. Saïd Business School, University of Oxford, Park End Street OX1 1HP, UK (email: )
2. Harvard Business School, Soldiers Field, Boston, MA 02163 (email: )
3. Department of Finance, Università Bocconi, and IGIER, Via Roentgen 1, 20136 Milan, Italy (email: )
4. Department of Economics, Harvard University, 1805 Cambridge Street, Cambridge MA 02138 (email: )