RT Journal Article SR Electronic T1 Once-only flexible sigmoidoscopy screening for colorectal cancer may not reduce colorectal cancer incidence or mortality JF Evidence Based Medicine JO Evid Based Med FD BMJ Publishing Group Ltd SP 171 OP 171 DO 10.1136/ebm.14.6.171 VO 14 IS 6 YR 2009 UL http://ebm.bmj.com/content/14/6/171.abstract AB