Department of Statistics and Probability, Michigan State University, 619 Red Cedar Road, Rm C432, East Lansing, MI 48824, USA. Tel.: +1-517-432-7098, Fax: +1-517-432-1405, cui@stt.msu.edu.|Department of Statistics and Probability, Michigan State University, 619 Red Cedar Road, Rm C432, East Lansing, MI 48824, USA. Tel.: +1-517-432-7098, Fax: +1-517-432-1405, cui@stt.msu.edu.