[1] Sacramento VAMC, Gastroenterol Sect, Mather, CA USA
[2] Univ Calif Davis, CTSC, Dept Publ Hlth, Div Biostat, Sacramento, CA USA
[3] VAGLAHS, Sepulveda Ambulatory Care Ctr, Los Angeles, CA USA
[4] Univ Calif Los Angeles, David Geffen Sch Med, Los Angeles, CA 90095 USA