Sarah Crook1, Milo A Puhan2, Anja Frei2. 1. Epidemiology, Biostatistics and Prevention Institute, Dept of Epidemiology, University of Zurich, Zurich, Switzerland sarah.crook@uzh.ch. 2. Epidemiology, Biostatistics and Prevention Institute, Dept of Epidemiology, University of Zurich, Zurich, Switzerland.