1. Department of Otorhinolaryngology, Päijät-Häme Central Hospital, Lahti, Finland
2. Department of Otolaryngology, Oslo University Hospital, Rikshospitalet, Oslo, Norway
3. Department of Otolaryngology and Communication Enhancement Boston Children’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
4. Department of Otorhinolaryngology, Tampere University Hospital and the University of Tampere, Tampere, Finland