[1] Univ Penn, Div Gastroenterol, Philadelphia, PA 19104 USA
[2] Univ Wisconsin, Sch Med, Sect Gastroenterol & Hepatol, Madison, WI USA
[3] Univ Penn, Renal Electrolyte & Hypertens Div, Philadelphia, PA 19104 USA
[4] Univ Penn, Dept Epidemiol & Biostat, Philadelphia, PA 19104 USA
[5] Univ Penn, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA