1. Department of Otorhinolaryngology–Head and Neck Surgery Turku University and Turku University Hospital Turku Finland
2. Department of Otorhinolaryngology–Head and Neck Surgery Helsinki University Hospital and University of Helsinki Helsinki Finland
3. Department of Clinical Medicine, Biostatistics Turku University and Turku University Hospital Turku Finland
4. Department of Otorhinolaryngology–Head and Neck Surgery Tampere University Hospital Tampere Finland
5. Department of Otorhinolaryngology–Head and Neck Surgery Oulu University Hospital Oulu Finland
6. Department of Otorhinolaryngology–Head and Neck Surgery Kuopio University Hospital Kuopio Finland