1. Department of Otorhinolaryngology and Head and Neck Surgery, Oulu University Hospital, Oulu, Finland
2. PEDEGO Research Unit, University of Oulu, Finland and Medical Research Centre Oulu, Oulu, Finland;
3. Division of Operative Care and Medical Research Centre Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland;
4. Audiological Research Centre, Faculty of Medicine and Health, Örebro University, Örebro, Sweden