1. Sloan School of Management, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142;
2. Yale School of Management, Yale University, New Haven, Connecticut 06511;
3. Google Research, New York, New York 10011;
4. University of Toronto Scarborough, Scarborough, Ontario M1C 1A4, Canada;
5. Rotman School of Management, University of Toronto, Toronto, Ontario M5S 3E6, Canada