1. Department of Chronic Diseases; Division of Epidemiology ; Norwegian Institute of Public Health; Oslo Norway
2. Epidemiology Branch; Division of Intramural Research ; National Institute of Environmental Health Sciences; National Institutes of Health; Department of Health and Human Services; Research Triangle Park North Carolina
3. Department of Global Public Health and Primary Care ; Medical Faculty; University of Bergen; Bergen Norway
4. Department of Community Medicine ; Medical Faculty; University of Oslo; Oslo Norway