1. Institute of Environmental Medicine, Division of Epidemiology, Karolinska Institute, 17177 Stockholm, Sweden
2. Institute of Environmental Medicine, Unit of Biostatistics, Karolinska Institutet, 17177 Stockholm, Sweden
3. Department of Clinical Science and Education, Stockholm South General Hospital, Karolinska Institutet, 11883 Stockholm, Sweden
4. Sachs’ Children and Youth Hospital, Stockholm South General Hospital, Karolinska Institutet, 11883 Stockholm, Sweden
5. Centre for Epidemiology and Community Medicine, Stockholm County Council, P.O. Box 1497, 17129 Stockholm, Sweden