1. Paediatric Research Center, Children’s Hospital, University of Helsinki, Helsinki University Hospital, Helsinki, Finland
2. Ilmarinen Mutual Pension Insurance Company, Helsinki, Finland
3. Department of Neurosurgery, Helsinki University Hospital, Helsinki, Finland
4. Department of Medicine, South Karelia Central Hospital, Lappeenranta, Finland
5. Research Department, Social Insurance Institution of Finland, Turku, Finland
6. Department of General Practice and Unit of Primary Health Care, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
7. Department of Pediatrics, Päijät-Häme Central Hospital, Lahti, Finland