1. Lund University, Faculty of Medicine, Department of Clinical Sciences-Lund, Orthopedics, Clinical Epidemiology Unit, Lund, Sweden;
2. Preventive Medicine and Public Health Research Center, Department of Community Medicine, Iran University of Medical Sciences, Tehran, Iran;
3. Epidemiology and Register Centre South, Skåne University Hospital Lund, Lund, Sweden;
4. Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston, MA, USA