1. Department of Family Medicine and Population Health, Division of Epidemiology, Virginia Commonwealth University, Richmond, Virginia.
2. Institute of Health and Society, Research Centre for Habilitation and Rehabilitation Models and Services (CHARM), Faculty of Medicine, University of Oslo, Oslo, Norway.
3. Department of Physical Medicine and Rehabilitation, Oslo University Hospital, Ulleval, Norway.
4. Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
5. Department of Research, Sunnaas Rehabilitation Hospital, Nesoddtangen, Norway.