1. Umeå University, Department of Public Health & Clinical Medicine, Occupational and Environmental Medicine, SE-901 87 Umeå, Sweden
2. Sahlgrenska University Hospital, Department of Occupational and Environmental Medicine, Box 414, SE-405 30 Gothenburg, Sweden
3. University Hospital of Northern Sweden, Department of Biomedical Engineering and Informatics, SE-901 85 Umeå, Sweden
4. Sundsvall Hospital, Department of Occupational and Environmental Medicine, Sundsvall, SE-851 86 Sweden