1. Section for Occupational and Environmental Health Department of Medicine, Karolinska Institute Huddinge University Hospital-R64, S-141 86, Huddinge, Sweden
2. National Institute for Psychosocial Factors and Health (IPM), Box 230, S-171 77, Stockholm, Sweden
3. Ericsson Research and Development, , Box 1505, S-125 25, Älvsjö, Sweden