1. Department of Epidemiology; Harvard T.H. Chan School of Public Health; Boston Massachusetts
2. Department of Health Management and Health Economy; Institute of Health and Society, University of Oslo; Oslo Norway
3. Centre for Clinical Research, Vårdcentralen Värmlands Nysäter; Värmland County Sweden
4. Department of Medical Epidemiology and Biostatistics; Karolinska Institutet; Stockholm Sweden
5. Department of Pediatrics; Örebro University Hospital; Örebro Sweden