1. Physiotherapy Department, University of Deusto, San Sebastian, Spain
2. Mugi Fisioterapia, Sabino Arana 30, Sopelana, Spain
3. School of Health and Rehabilitation Sciences, Department of Physiotherapy, University of Queensland, St Lucia, Queensland, Australia
4. Research Group on Statistics, Econometrics and Health (GRECS), University of Girona, Girona, Spain
5. CIBER of Epidemiology and Public Health (CIBERESP), Madrid, Spain
6. Physiotherapy, Department of Physiology, Faculty of Medicine and Nursing, University of the Basque Country UPV/EHU, Leioa, Spain