1 Institute of General Practice and Evidence-based Health Services Research, Medical University of Graz, 8036 Graz, Austria; Department of Health Services Research and Policy, Faculty of Public Health and Policy, London School of Hygiene & Tropical Medicine, London, UK; Steiermärkische Gebietskrankenkasse, Graz, Austria. Electronic address: florian.stigler@medunigraz.at.
2 Research Department of Epidemiology and Public Health, University College London, London, UK.