1. Department of Management Science and Engineering, Stanford University, Stanford, California 94305;
2. Department of Management Science and Information Systems, Guanghua School of Management, Peking University, Beijing 100871, China;
3. The Robert H. Smith School of Business, Institute for Systems Research, University of Maryland, College Park, Maryland 20742;
4. Department of Management Science, School of Management, Fudan University, Shanghai 200433, China