1 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada L8S 4L8 Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
2 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada L8S 4L8 Division of General Internal Medicine, and Division of Clinical Epidemiology, University Hospitals of Geneva, Geneva, Switzerland.
3 The BMJ, London WC1H 9JP, UK.
4 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada L8S 4L8 Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8S 4L8.
5 Institute of Health and Society, Faculty of Medicine, University of Oslo, 0318 Oslo, Norway.
6 Institute of Health and Society, Faculty of Medicine, University of Oslo, 0318 Oslo, Norway Department of Medicine, Innlandet Hospital Trust-division, Gjøvik, Norway [email protected].