[1] Finnish Inst Hlth & Welf, Populat Hlth Unit, Helsinki, Finland
[2] Univ Helsinki, Childrens Hosp, Helsinki, Finland
[3] Helsinki Univ Hosp, Helsinki, Finland
[4] Finnish Inst Hlth & Welf, Informat Serv, Helsinki, Finland
[5] Reg Stockholm, Acad Primary Hlth Care Ctr, Stockholm, Sweden
[6] Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden
[7] Oulu Univ Hosp, PEDEGO Res Unit, Oulu, Finland
[8] Univ Oulu, Oulu, Finland
[9] Norwegian Univ Sci & Technol, Dept Clin & Mol Med, Trondheim, Norway