[1] Helsinki City Hlth Ctr, Kallio Hlth Stn, Helsinki, Finland
[2] Finnish Patient Insurance Ctr, Helsinki, Finland
[3] Reg State Adm Agcy Southern Finland, Helsinki, Finland
[4] Natl Supervisory Author Welf & Care, Helsinki, Finland
[5] Univ Helsinki, Cent Hosp, Dept Otorhinolaryngol Head & Neck Surg, Helsinki, Finland