[gwd]

Right, so to properly isolate the effect of the colonoscopy on mortality, we need to do a randomized trial with just people like you -- people who would definitely get a colonoscopy if invited -- to see what the effect is. Because you're also more likely to act on early warning signs and get a cancer diagnosis in time to treat the cancer rather than die.

[robertlagrant]

> Because you're also more likely to act on early warning signs and get a cancer diagnosis in time to treat the cancer rather than die.

This seems to imply we should discount all treatments because people who choose to get treatment are more likely to get better, coincidentally by the same amount as the treatment's efficacy.

[gwd]

That's not what it means at all.

The question here is a question that the medical establishment is trying to answer: namely, "What can we, as the medical establishment do, to reduce deaths from colon cancer?" For a long time, the answer has been, "Invite people to take colonscopies". What the data here appears to show is that the action, "Invite people to take colonoscopies" doesn't actually reduce deaths from colon cancer. If the medical establishment wants to actually reduce deaths from colon cancer, they'll need to figure out something else.

I guess I do agree that the headline is likely to be counterproductive. What the data might show is that the most effective thing you as an individual can do is to be the kind of person who takes colonoscopies when invited. The unfortunate effect it might have is to make more people into the kind of people who don't take colonoscopies when invited.

[robertlagrant]

> I guess I do agree that the headline is likely to be counterproductive. What the data might show is that the most effective thing you as an individual can do is to be the kind of person who takes colonoscopies when invited. The unfortunate effect it might have is to make more people into the kind of people who don't take colonoscopies when invited.

Agreed. Except the most effective thing you can do as an individual is have a colonoscopy, not be the sort of person who would have one :-)

[gwd]

> Except the most effective thing you can do as an individual is have a colonoscopy, not be the sort of person who would have one :-)

So we have two hypotheses here:

1. Having the colonoscopy is the thing that reduces deaths from colon cancer

2. Having the colonoscopy correlates to some other factor, X; and it's actually X which reduces the deaths from colon cancer.

X, for instance, could be a high willingness / ability to see the doctor when you experience early symptoms of colon cancer. That is, the more willing you are to go to the doctor when you start to have early symptoms of colon cancer, the more likely you are to survive it; and the more willing/able you are to go to the doctor when you have early symptoms of colon cancer, the more willing/able you are to have a colonoscopy.

What evidence do you have to believe that #1 is true, rather than #2?

Because if #1 is the case, the medical system should push hard on colonoscopies. But if #2 is the case, pushing colonoscopies might be a red herring. In fact, it might be counterproductive -- I've heard that colonoscopies are unpleasant; if you pressure people who don't like doctors into having a colonoscopy, and they have a terrible experience, then when they experience early symptoms of colon cancer, they may be more likely to procrastinate to avoid having another one. Rather, if #2 is the case, the medical system should try find out what can be done to make people more willing / able to get early medical care.

[vidarh]

No, but you need to account for it when considering efficacy, because people who choose to follow through on treatments may also be taking other steps that may also improve their outcomes, and it can be hard to tease out because the mere act of telling them they should have a screening might change other behaviours even without being prompted by doctors in a way that's recorded.

E.g. it's a reasonable hypothesis that patients who are more motivated to show up might also be more motivated to look up possible causes and what other steps they can take to improve their chances.

In other words, it's reasonable to expect people who comply to potentially get better at a higher rate than the efficacy of a single treatment, and teasing out how much of this effect is due to the intervention itself and how much is due to changed behaviour due to the referral is hard.