1. Department of Biostatistics, School of Public Health; Yale University; 60 College Street New Haven CT 06520 U.S.A.
2. Department of Statistics and Probability; Michigan State University; 619 Red Cedar Rd East Lansing MI 48824 U.S.A.
3. VA Cooperative Studies Program Coordinating Center; West Haven CT 06516 U.S.A.
4. Data Mining Research Center, School of Economics; Xiamen University; Xiamen China