1. Oslo Centre for Biostatistics and Epidemiology, Department of Biostatistics , University of Oslo , Oslo , Norway
2. Department of Community Medicine, Department of Community Medicine , 8016 UiT The Arctic University of Norway , Tromsø , Norway
3. Department of Public Health and Nursing, K.G. Jebsen Center for Genetic Epidemiology , 8016 UiT The Arctic University of Norway , Trondheim , Norway