1. Department of Epidemiology; Biostatistics and Occupational Health; McGill University; Montreal QC Canada
2. Centre for Clinical Epidemiology; Lady Davis Institute for Medical Research; Jewish General Hospital; Montreal QC Canada
3. Department of Pediatrics; McGill University; Montreal QC Canada
4. Department of Obstetrics and Gynecology; McGill University; Montreal QC Canada
5. Department of Epidemiology; University of Pittsburgh; Pittsburgh PA USA