1. Institute of General Practice and Family Medicine, University Hospital Bonn, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
2. Nursing Research Unit, Institute for Social Medicine and Epidemiology, University of Lübeck, Ratzeburger Allee 160, 23562 Luebeck, Germany
3. uzbonn, Survey Center Bonn—Center for Empirical Social Research and Evaluation, Oxfordstraße 15, 53111 Bonn, Germany