From the McGill University, Montreal, Quebec, Canada.
Editors’ note: This series addresses topics of interest to epidemiologists across a range of specialties. Commentaries start as invited talks at symposia organized by the Editors. This symposium took place at the Third North American Congress of Epidemiology in Montreal in June 2011 and was organized by Editors Kaufman and Hernán.
Correspondence: Jay S. Kaufman, Department of Epidemiology, Biostatistics, & Occupational Health, Purvis Hall, 1020 Pine Ave. West, Rm 45 Montreal, QC H3A 1A2, Canada. E-mail: firstname.lastname@example.org.