1. Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, 450 Brookline Ave, Boston, MA 02215, USA and Department of Biostatistics, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA 02115, USA
2. Genetech, Product Development Biostatistics, 1 DNA Way, South San Francisco, CA 94080, USA
3. Department of Computer Science, University of Maryland, College Park, USA and Center for Bioinformatics and Computational Biology, Institute of Advanced Computer Studies, University of Maryland, 8314 Paint Branch Dr., College Park, MD 20742, College Park, USA