J André Knottnerus1, Peter Tugwell2. 1. Department of General Practice, Netherlands School of Primary Care Research, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands. Electronic address: anneke.germeraad@maastrichtuniversity.nl. 2. Department of Medicine, Department of Epidemiology and Community Medicine, Canada Research Chair, University of Ottawa, Institute of Population Health, Ottawa, ON, Canada.