1. Institute for Research in Operative Medicine Witten/Herdecke University Ostmerheimer Str 200, Building 38 51109 Cologne Germany
2. Institute of Medical Biometry and Informatics University of Heidelberg Heidelberg Germany
3. Institute for Biometrics and Epidemiology, German Diabetes Center Leibniz Institute for Diabetes Research at Heinrich Heine University Düsseldorf Düsseldorf Germany
4. Institute of Medical Statistics Düsseldorf University Hospital and Medical Faculty, Heinrich Heine University Düsseldorf Düsseldorf Germany