1. School of StatisticsSouthwestern University of Finance and Economics Chengdu, Sichuan 611130 China
2. School of Mathematics and StatisticsThe University of Melbourne Parkville, VIC 3010 Australia
3. Department of Operations Research and Financial EngineeringPrinceton University Princeton, New Jersey 08544 U.S.A.
4. Department of StatisticsColorado State University Fort Collins, Colorado 80523 U.S.A.