1. Biostatistical Department, U717 Inserm, AP-HP, Paris 7 University, Saint-Louis Hospital, 1 Avenue Claude Vellefaux, 75475 Paris Cedex 10, France,
2. Biostatistical Department, U717 Inserm, AP-HP, Paris 7 University, Saint-Louis Hospital, 1 Avenue Claude Vellefaux, 75475 Paris Cedex 10, France