1. Clinic for Paediatrics, Evangelic Hospital Hamm, Hamm, Germany;
2. Clinical Research Department, Dr. Willmar Schwabe GmbH & Co. KG, Karlsruhe, Germany;
3. Clinic for Paediatrics, Charité - Universitätsmedizin Berlin, Berlin, Germany;
4. Institute for Medical Statistics, Informatics and Epidemiology of the University of Cologne, Cologne, Germany