1 Department of Statistics, Seoul National University, Gwanak_1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Republic of Korea.
2 Montefiore Institute, Université de Liège, Bâtiment B28, Office 0.15-B37, Grande Traverse 10, 4000 Liège, Belgium.
3 Department of Biostatistics, University of Alabama at Birmingham, Ryals Public Health Building, No. 420B, Birmingham, AL 35294, USA.
4 Division of Biostatistics, Human Genetics Center, School of Public Health, The University of Texas Health Science Center at Houston, 1200 Herman Pressler, Houston, TX 77030, USA.