1. Department of Statistical Science, University College London, 1-19 Torrington Place, London WC1E 7HB, UK
2. Department of Economics and Statistics, University of Torino, Corso Unione Sovietica 218/bis, Torino 10134, Italy
3. Oncology Biostatistics and Bioinformatics, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, 550 N. Broadway, Suite 1103, Baltimore, MD 21205, USA