1. Department of Genes and Environment; Division for Epidemiology; Norwegian Institute of Public Health; Oslo Norway
2. Norwegian Resource Centre for Women's Health; Rikshospitalet; Oslo Norway
3. Division for Epidemiology; Norwegian Institute of Public Health; Oslo Norway
4. Department of Mathematics; University of Oslo; Oslo Norway
5. International School of Public Health; Northern State Medical University; Arkhangelsk Russia
6. Department of International Public Health; Norwegian Institute of Public Health; Oslo Norway