1. General Surgery Unit, ASST-Brianza, Vimercate Hospital, Via Santi Cosma e Damiano, 10, 20871 Vimercate, Italy
2. General Surgery Residency Program, University of Milan, Via Festa del Perdono, 7, 20122 Milan, Italy
3. General Surgery Residency Program, University of Pavia, Corso Str. Nuova, 65, 27100 Pavia, Italy
4. General Surgery Unit, Department of Surgery, Fondazione I.R.C.C.S. Policlinico San Matteo, Viale Camillo Golgi, 19, 27100 Pavia, Italy
5. Center of Biostatistics for Clinical Epidemiology, University of Milan—Bicocca, Via Cadore, 48, 20854 Monza, Italy