1. Olli Saarela is Associate Professor, Dalla Lana School of Public Health, University of Toronto, 155 College Street, Toronto, Ontario M5T 3M7, Canada
2. David A. Stephens is Professor, Department of Mathematics and Statistics, McGill University, Burnside Hall, 805 Sherbrooke Street West, Montreal, Quebec H3A 0B9, Canada
3. Erica E. M. Moodie is Professor, Department of Epidemiology and Biostatistics, McGill University, 2001 McGill College Ave, Montreal, Quebec H3A 1G1, Canada