Department of Statistical Science, University of Toronto, Toronto, ON, Canada, Program in Child Health Evaluative Sciences, the Hospital for Sick Children Research Institute, Toronto, ON, Canada, Department of Clinical Neuroscience, Institute of Psychiatry, Kings College London, London, Division of Genetics and Epidemiology, Institute of Cancer Research, Sutton, Surrey, Molecular and Population Genetics and NIHR Comprehensive Biomedical Research Centre, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK, Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.