[1] Med Univ S Carolina, Ctr Hlth Care Res, Charleston, SC 29425 USA
[2] Mayo Clin, Div Area Gen Internal Med, Rochester, MN USA
[3] Mayo Clin, Div Gastroenterol, Rochester, MN USA
[4] Mayo Clin, Clin Epidemiol Sect, Rochester, MN USA
[5] Mayo Clin, Biostat Sect, Rochester, MN USA
[6] Univ Western Ontario, Dept Med, London, ON, Canada
[7] Univ Western Ontario, Dept Epidemiol & Biostat, London, ON, Canada