[1] Univ Autonoma Madrid, Dept Gastroenterol, Puerta de Hierro Hosp, Madrid, Spain
[2] Univ Autonoma Madrid, Dept Biostat, Puerta de Hierro Hosp, Madrid, Spain
[3] Univ Autonoma Madrid, Clin Epidemiol Unit, Puerta de Hierro Hosp, Madrid, Spain
[4] Univ Oviedo, Dept Gastroenterol, Hosp Cent Asturias, Oviedo, Spain
[5] Univ Valencia, Dept Gastroenterol, Hosp La Fe, Valencia, Spain
[6] Leon Hosp, Dept Gastroenterol, Leon, Spain
[7] Rey Juan Carlos Univ, Dept Gastroenterol, Alcorcon Fdn Hosp, Alcorcon, Spain