1. Wang Yanan Institute for Studies in Economics (WISE), Department of Statistics, School of Economics and Fujian Key Laboratory of Statistical Science, Xiamen University, Xiamen, Fujian, China
2. Department of Statistics and Applied Probability, University of California at Santa Barbara
3. Department of Biostatistics, Yale University, New Haven, Connecticut, U.S.A.; and Wang Yanan Institute for Studies in Economics (WISE), Department of Statistics and School of Economics, Xiamen University, Xiamen, Fujian, China