Klaus Kaier1, Martin Wolkewitz2, Thomas Heister2. 1. Division Methods in Clinical Epidemiology, Institute of Medical Biometry and Statistics, Faculty of Medicine and Medical Center-University of Freiburg, Freiburg, Baden-Württemberg, Germany. Electronic address: kaier@imbi.uni-freiburg.de. 2. Division Methods in Clinical Epidemiology, Institute of Medical Biometry and Statistics, Faculty of Medicine and Medical Center-University of Freiburg, Freiburg, Baden-Württemberg, Germany.