[JamesBarney]

When everyone invited for a colonoscopy is compared to the control group 42% showed up and got a colonoscopy 18% fewer people got colon cancer same number of people died of colon cancer

When everyone who got a colonoscopy is compared to the control group 30% fewer got colon cancer 50% fewer people died of colon cancer

This data makes me think the mortality reduction benefit is bogus, but the cancer prevention benefit is real, and probably greater than 18%, maybe closer to 36-40%. If the colon cancer mortality benefit was real you'd see some reduction in the intention to treat group, and it'd be smaller than the cancer prevention effect. (The most aggressive cancers tend to be harder cancers to catch in time because they most so quickly, so most cancer screening tests will prevent more cancers than deaths)