1. Clinical Epidemiology and Biostatistics, School of Medical Sciences; Örebro University; Örebro Sweden
2. Clinical Epidemiology Unit, Department of Medicine; Karolinska Institute; Sweden
3. Department of Epidemiology and Public Health; University College London; London United Kingdom
4. Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institute; Stockholm Sweden
5. Division of Childhood Cancer Research, Department of Women's and Children's Health; Karolinska Institute; Stockholm Sweden