1. Faculty of Medicine, University of Belgrade, Belgrade, Serbia
2. Clinic for Otorhinolaryngology and Maxillofacial Surgery, University Clinical Centre Serbia, Belgrade, Serbia
3. Clinic for Otorhinolaryngology, University Clinical Centre Kragujevac, Kragujevac, Serbia
4. Department of Otorhinolaryngology, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia
5. Institute for Biomedical Statistics, Faculty of Medicine, University of Belgrade, Belgrade, Serbia