[1] Univ Turku, Dept Paediat Surg & Orthopaed, Turku, Finland
[2] Turku Univ Hosp, Turku, Finland
[3] Kuopio Univ Hosp, Dept Paediat Surg, Kuopio, Finland
[4] Finnish Inst Hlth & Welf, Informat Serv Dept, Helsinki, Finland
[5] Univ Turku, Dept Biostat, Turku, Finland
[6] Kuopio Univ Hosp, Dept Paediat, Kuopio, Finland
[7] Karolinska Inst, Dept Neurobiol Care Sci & Soc, Stockholm, Sweden
[8] Tampere Univ Hosp, Dept Paediat Surg, Tampere, Finland
[9] Tampere Univ, Tampere, Finland