1. University of Oxford; Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences (NDORMS); John Radcliffe Hospital Headley Way Oxford UK OX3 9DU
2. Thomas Jefferson University Hospital; Department of Surgery; 1100 Walnut Street Philadelphia PA USA 19107
3. Howard-Harvard Health Sciences Outcomes Research Center Howard University College of Medicine; Department of Surgery; 2041 Georgia Ave, NW Washington DC USA 20060
4. University of Oxford; Nuffield Department of Population Health; Big Data Institute, Old Road Campus Oxford UK OX3 7LF
5. Saxion University of Applied Sciences; Social Work Research Group; Enschede Netherlands
6. Norwegian Institute of Public Health; PO box 222 Skøyen Oslo Norway 0213
7. University of Oslo; Institute of Health and Society; P.O box 1130 Blindern Oslo Norway 0318