Study realised by Christophe Daniel (GRANEM, Angers University), Anne Lavigne (LEO, Orléans University), Stéphane Mottet (GRIEF, Poitiers University), Jésus-Herell Nze Obame (GRANEM, Angers University), Bruno Séjourné (GRANEM, Angers University), Christian Tagne (LEO, Orléans University)