1 Department of Epidemiology & International Public Health, School of Public Health, Bielefeld University, P. O. Box 100131, 33501, Bielefeld, Germany. oliver.razum@uni-bielefeld.de.
2 Health Policy and Health Services Research Group, Health Policy Research Unit, Consorci de Salut i Social de Catalunya, Avenida Tibidabo, 21, 08022, Barcelona, Spain.