Department of Biostatistics, Johns Hopkins School of Public Health, Baltimore, MD, USA.|Institut de Recherches Cliniques de Montréal, Montreal, Quebec H2W 1R7, Canada.|Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario M5G 1L7, Canada and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.|Department of Biostatistics, Johns Hopkins School of Public Health, Baltimore, MD, USA.