[DanBC]

It's pretty hard to ignore that extra information though.

You run a screening company. You take people at high risk of lung cancer -- people who smoke a lot and have smoked a lot for many years -- and you provide low dose CT scans of their lungs.

Bob comes in. You scan his lungs and you find spots.

What do you do now?

You're probably going to start providing treatment to Bob. Will this help Bob live longer? Will it improve his quality of life? It might not.

https://blogs.bmj.com/bmjebmspotlight/2019/02/15/understandi...

[TeMPOraL]

> What do you do now?

Hopefully get other tests done, to confirm diagnosis.

I'm with GP here. I can't understand this attitude either. Having more information should never make you more wrong. This holds for uncertain information, because uncertainty can be quantified and tracked (if you're not doing this, then you're doing voodoo, not science).

I can see two reasons why you wouldn't want to gather more information in medical context. One, many tests carry risk to patient's health and well-being, so there's no point of doing them if that risk outweighs the expected value of evidence gathered. Two, I suspect that gathering information also gathers legal obligations and risks to doctors.

[DanBC]

> Hopefully get other tests done, to confirm diagnosis

Those other tests involve things like "needle biopsy" -- they shove a needle through your chest into your lung into the suspect tissue to get a sample. This carries risk. We can justify that risk if it saves life. But this is the problem with screening -- often it doesn't save life (of course, it depends on the type of screening).

https://www.radiologyinfo.org/en/info.cfm?pg=nlungbiop

> Having more information should never make you more wrong

But you can see how having lots of low-quality information could make someone more wrong -- these are not clear signals, because if they were it wouldn't be a problem. These are almost noise. We're taking data from a large population ("4 in 100 people with this result have this disease") and trying to apply it to the individual, and when we try to get more information we subject this person to more radiation in scans or invasive procedures or both. We increasing the risk, but not necessarily saving life.

> there's no point of doing them if that risk outweighs the expected value of evidence gathered

Yes, this is exactly the balance that doctors are making. They're looking at all cause mortality and seeing if life is saved.