1. Centre for Health Equity Studies (CHESS) Stockholm University/Karolinska Institutet 106 91 Stockholm Sweden
2. Clinical Epidemiology Department of Medicine Karolinska Institutet 171 77 Stockholm Sweden
3. Nordic School of Public Health Box 12133, 402 42 Göteborg Sweden
4. Department of Women's and Children's Health Uppsala University Uppsala Akademiska Hospital 751 85 Uppsala Sweden