1. Department of Surgery and Medical-Surgical Specialities, School of Medicine and Dentistry, University of Santiago de Compostela, Santiago de Compostela, Spain
2. Methodology and Statistics Unit, Ramón Domínguez Foundation for R+D+i in Healthcare Sciences. Santiago de Compostela University Hospital, Santiago de Compostela, Spain
3. Department of Surgery and Medical-Surgical Specialities, School of Medicine and Health Sciences, University of Oviedo, Oviedo, Spain
4. CS Praza do Ferrol, EOXI Lugo, Cervo, e Monforte, Galician Health Service, Lugo, Spain