1. St George's, University of London; Population Health Sciences and Education; Cranmer Terrace London UK SW17 0RE
2. McMaster University; Department of Medicine and Department of Clinical Epidemiology and Biostatistics; 301 James Street South Hamilton, Ontario Canada L8P3B6
3. IMIM (Hospital del Mar Medical Research Institute); Health Services Research Unit; Doctor Aiguader 88 Barcelona Spain 08003