Department of Statistics, Inha University, Incheon, Korea.|Department of Statistics, Seoul National University, Seoul, Korea.|Department of Statistical Science, Southern Methodist University, 6425 Boaz Lane, Dallas, TX 75205, USA.|Department of Biostatistics, University of Florida, 2004 Mowry Road, Gainesville, FL 32611, USA.|Department of Clinical Sciences, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA. guanghua.xiao@utsouthwestern.edu.