1 Department of Primary Care and Public Health, School of Public Health, Imperial College London, London, United Kingdom; Department of Medicine I, Rheinisch-Westfälische Technische Hochschule University Hospital Aachen, Aachen, Germany. Electronic address: jbrandts@ukaachen.de.
2 Department of Primary Care and Public Health, School of Public Health, Imperial College London, London, United Kingdom. Electronic address: k.ray@imperial.ac.uk.