[1] Univ Penn, Ctr Clin Epidemiol & Biostat, 720 Blockley Hall ,423 Guardian Dr, Philadelphia, PA 19104 USA
[2] Univ Penn, Div Gastroenterol, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[4] Univ Colorado, Div Gastroenterol, Anschutz Med Campus, Aurora, CO USA
[5] Univ Penn, Abramson Canc Ctr, Philadelphia, PA 19104 USA
[6] Univ Alabama Birmingham, Dept Epidemiol, Birmingham, AL USA
[7] Univ Alabama Birmingham, Div Clin Immunol & Rheumatol, Birmingham, AL USA