1. Sloan School of Management, Massachusetts Institute of Technology, 30 Memorial Drive, Cambridge, Massachusetts, U.S.A
2. Department of Mathematics, Imperial College London, 545 Huxley Building, South Kensington Campus, London, U.K
3. Department of Operations Research and Financial Engineering, Princeton University, 205 Sherred Hall, Princeton, New Jersey, U.S.A
4. Department of Biostatistics, University of North Carolina at Chapel Hill, 3105D McGavran-Greenberg Hall, Chapel Hill, North Carolina, U.S.A