[pbourke]

In this case they are examining colon cancer and deaths from it, and the colonoscopy is a diagnostic test for colon cancer. I feel that the results are being presented to the public in a very misleading way. People will read this headline and conclude that they don’t need to get a colonoscopy which I don’t think follows from this study at all.

[gwd]

> People will read this headline and conclude that they don’t need to get a colonoscopy which I don’t think follows from this study at all.

What this appears to show is that you need to get a colonoscopy to avoid colon cancer; but that you don't need to get a colonoscopy to avoid death. I'd much rather avoid colon cancer entirely than have colon cancer and survive.

But as GP pointed out, maybe you need something else to avoid death: something that is correlated with responding to the invitation to get a colonoscopy. Maybe if you're willing and able to get a colonoscopy when invited, you're willing and able to more pro-actively go to the doctor when you notice other issues that are indicative of colon cancer, allowing you to get early treatment. And conversely, maybe if you're not willing or able to get a colonoscopy when invited, you're more likely to ignore symptoms until it's too late.

Again, avoiding colon cancer in the first place is better than successfully treating it; but it does point to the fact that other interventions might be more helpful in actually preventing deaths.

[kashunstva]

> And conversely, maybe if you're not willing or able to get a colonoscopy when invited, you're more likely to ignore symptoms until it's too late.

Yes. This is the argument against relying on the secondary analysis in this study. Although the invited and standard care groups were randomized such that differences in putative confounders were adjusted for, the rejection of the intervention itself may have reintroduced systematic differences that reduce the reliability of the hypothesis that intention to screen for colon cancer reduces mortality. Possibly those who accepted screening colonoscopy are more attentive to other health and lifestyle practices that reduce colon cancer mortality.

[divbzero]

I agree. Even if intention-to-treat is the gold standard endpoint for trials, a more accurate and nuanced headline for the general public would be:

Inviting patients to undergo screening colonoscopy fails to reduce rate of cancer deaths

[pessimizer]

Or: If you compare a group of people who never get colonoscopies with a group of people containing many who do get colonoscopies, the same number of people die.

Imagine two cages filled with identical mice. One you drop some food into, and the other you don't. They starve to death at the same rate. Surprised?

[JamesBarney]

The study results are "colonoscopies do not lead to a reduction in colon cancer mortality". Reporting that isn't misleading that's what the study says.

Basically in the treated group of 1103 of every 10,000 people died. And in the control group 1104 of every 10,000 people died.

So to summarize the study. Inviting someone to a colonoscopy reduces their risk of getting colon cancer by 22 basis points. Their risk of dying from colon cancer by 3 basis points, and their risk of dying of any cause by 1 basis point.

With the actual risk reduction being up to 5x this assuming it's a 20% difference in the rate of getting colonoscopies which is driving the difference.

But this makes metformin look good because it drives a much larger overall reduction in risk.

[pbourke]

> The study results are "colonoscopies do not lead to a reduction in colon cancer mortality". Reporting that isn't misleading that's what the study says.

The measured intervention was not the colonoscopy, it was the invitation to screen. Only 42% of invited patients actually got a colonoscopy. This is far more persuasive to me:

> "When the investigators compared just the 42% of participants in the invited group who actually showed up for a colonoscopy to the control group, they saw about a 30% reduction in colon cancer risk and a 50% reduction in colon cancer death. “That adds to a bunch of observational study data that suggests exposing people to colonoscopy can reduce risk of developing and dying of colon cancer,” Gupta said."

As a member of the public, I don't really care about invitation to screen, but do care about the efficacy of colonoscopy. I can see invitation to screen being an important concern from a public health standpoint.

[JamesBarney]

The problem is whether or not they chose to get a colonoscopy is a confounding variable which inflates the value of the colonoscopy when some of the results are driven by other attributes.