[1] Mayo Clin & Mayo Fdn, Gastroenterol Res Unit, Sect Colon & Rectal Surg, Rochester, MN 55905 USA
[2] Univ Sydney, Dept Med, Sydney, NSW 2006, Australia
[3] Univ Sydney, Nepean Hosp, Sydney, NSW 2006, Australia
[4] Mayo Clin & Mayo Fdn, Dept Biostat, Rochester, MN 55905 USA