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Table 1. Effect of Screening Intervention on Reducing Mortality from Colorectal Cancera

Screening Intervention Study Design Internal Validity Consistency Magnitude of Effects External Validity
Fecal Occult Blood TestRCTsGoodGood15%–33%Fair
SigmoidoscopyCase-control studies,[1] RCTs in progressFairFairAbout 60%–70% for left colonFair
Digital Rectal ExamCase-control studiesFairGoodNo effectPoor
ColonoscopyCase-control studies, RCTs in progressPoorPoorAbout 60%–70% for left colon; uncertain for right colonFair

RCT = randomized controlled trial.
aThere are no data on the effect of other screening interventions (i.e., fecal occult blood test combined with sigmoidoscopy, barium enema, colonoscopy, computed tomographic colonography, and stool DNA mutation tests) on mortality from colorectal cancer.


  1. Thiis-Evensen E, Hoff GS, Sauar J, et al.: Population-based surveillance by colonoscopy: effect on the incidence of colorectal cancer. Telemark Polyp Study I. Scand J Gastroenterol 34 (4): 414-20, 1999.  [PUBMED Abstract]