1. Limin Peng is Assistant Professor and Yijian Huang is Associate Professor , Department of Biostatistics, Rollins School of Public Health, Emory University, Atlanta, GA 30322. The authors thank the joint editors, the associate editor, and the referees for insightful comments on the manuscript. They are grateful to Professor Roger Koenker for his efforts in the timely implementation of the proposed methods in the R package quantreg. They also thank Dr. Nancy Kutner and Ms. Rebecca Hong Zhang for providing...