1. Department of Digestive Surgery, Hôpital Lariboisière, Paris, France
2. Department of Digestive Surgery, Hôtel-Dieu, Clermont-Ferrand, France
3. Department of Digestive Surgery, Hôpital Jean Minjoz, Besançon, France
4. Department of Statistics, Centre Jean Perrin, Clermont-Ferrand, France