1. Oslo Centre for Biostatistics and Epidemiology; Institute of Basic Medical Sciences; University of Oslo; P.O. Box 1122 Blindern N-0317 Oslo Norway
2. Department of Community Medicine; Faculty of Health Sciences; University of Tromsø; The Arctic University of Norway; Tromsø Norway
3. Department of Scientific Engineering and Safety; University of Tromsø; The Arctic University of Norway; Tromsø Norway
4. Department of Etiological Research; Cancer Registry of Norway; Oslo Norway
5. Department of Medical Epidemiology and Biostatistics; Karolinska Institutet; Stockholm Sweden
6. Department of Genetic Epidemiology; Folkhälsan Research Center; Helsinki Finland