1 Department of Epidemiology & Biostatistics, University of California, San Francisco, CA, USA. Electronic address: dennis.black@ucsf.edu.
2 Department of Epidemiology & Biostatistics, University of California, San Francisco, CA, USA.
3 Division of Clinical Medicine, School of Medicine and Population Health, University of Sheffield, Sheffield, UK.
4 Center for Advanced Orthopedic Studies, Beth Israel Deaconess Medical Center, Boston, MA, USA; Department of Orthopedic Surgery, Harvard Medical School, Boston, MA, USA.