1. Department of Otorhinolaryngology, Head and Neck Surgery, Essen University Hospital, University Duisburg-Essen, Essen, Germany
2. Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Marburg, Philipps-Universität Marburg, Marburg, Germany
3. Center of Clinical Epidemiology, Institute of Medical Informatics, Biometry and Epidemiology, Essen University Hospital, Essen, Germany