1. Department of StatisticsKangwon National UniversityChuncheonGangwon 24341South Korea
2. Statistical Research and Applications BranchDivision of Cancer Control and Population StudiesNational Cancer InstituteBethesdaMaryland 20892U.S.A.
3. Department of BiostatisticsUniversity of North Carolina at Chapel Hill Chapel Hill North Carolina 27599 U.S.A.
4. Department of StatisticsUniversity of North Carolina at Chapel Hill Chapel Hill North Carolina 27599 U.S.A.