1. Department of Statistical Sciences, University of Toronto, 100 St George Street, Toronto, Ontario, Canada
2. Department of Statistics, University of Illinois at Urbana-Champaign, 725 South Wright Street, Champaign, Illinois, USA
3. Department of Bioinformatics and Biostatistics, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang District, Shanghai, China
4. Department of Biostatistics, University of North Carolina at Chapel Hill, 3101 McGavran-Greenberg Hall, Chapel Hill, North Carolina, USA