1. a Department of Biostatistics and Bioinformatics , Duke University School of Medicine , Durham , North Carolina , USA
2. b Department of Statistics and Finance , University of Science and Technology of China , Anhui , China
3. c Department of Management Sciences , City University of Hong Kong , Hong Kong
4. d Global Biostatistics and Epidemiology , Amgen, Inc. , Thousand Oaks , California , USA