1. Department of Psychosomatics and Psychiatry, University Children's Hospital, Steinwiesstrasse 75, CH-8032, Zurich, Switzerland
2. Department of Psychosomatics and Health Behaviour, Norwegian Institute of Public Health, Nydalen, Oslo, Norway
3. Children's Hospital, Aarau, Switzerland
4. Department of Paediatrics, University Children's Hospital Zurich, Zurich, Switzerland