1. Pengfei Li is Assistant Professor, Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2G1 . Jiahua Chen is Professor, Department of Statistics, University of British Columbia, Vancouver, BC, Canada, V6T 1Z2 . The authors thank the editor, the associate editor, and three referees for constructive comments and suggestions that lead to significant improvements in the article. This research was supported by the Natural Sciences and Engineering Research...