Affiliation: | (1) Departamento de Gastroenterolog?a, Hospital de Especialidades, Centro M?dico Nacional Siglo XXI, IMSS, Av. Cuauhtemoc 330, Col. Doctores, 06725 Mexico, DF, Mexico;(2) Gastrointestinal Unit, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Warren 1007, Boston, MA 02114, USA;(3) Department of Medicine, John Hopkins University School of Medicine, Baltimore, MD, USA;(4) MGH Biostatistics Center, Harvard Medical School, Boston, MA, USA |