[1] Massachusetts Gen Hosp, Div Gastroenterol, Boston, MA 02114 USA
[2] Harvard Med Sch, Boston, MA 02115 USA
[3] Massachusetts Gen Hosp, Clin & Translat Epidemiol Unit, Boston, MA 02114 USA
[4] Univ Iowa, Coll Pharm, Dept Pharm Practice & Sci, Iowa City, IA USA
[5] Univ Iowa, Carver Coll Med, Dept Family Med, Iowa City, IA USA