4 ms·

> strong enough evidence This is actually a bit subtle. For example I've heard more than one radiologist claim that if you look carefully, literally anyone's

by ska 3y ago

> strong enough evidence This is actually a bit subtle. For example I've heard more than one radiologist claim that if you look carefully, literally anyone's body scan will contain details that could justify work up. The fact is, if you do this broadly in a population and you work up everything you see that would justify it, some small number of people will die or suffer serious problems from complications of follow up. This is a fundamental problem in screening technologies (of any kind) with imperfect sensitivity. You can't get away from this, so you try and be clear that the net benefit is (much) higher. I'm not even against the idea of baseline scans, but the idea that this part is simple is naive.

kragen 3y ago
that's just because the radiologists' standard for 'could justify work up' are too low
- ska 3y ago
  Or it's because the problem is genuinely hard. See above ('imperfect sensitivity')... the same problem exists in e.g. blood tests. I'm no radiologist but I've seen enough of this done that I'd lean that way. Especially if you consider realistic bounds on time and additional information.
  - kragen 3y ago
    yes, of course the problem is genuinely hard, but having less information about your body makes it harder, not easier
    - ska 3y ago
      In the abstract more information is always better. In practical healthcare with real constraints, sometimes it makes things worse globally for reason above. Think about say a diagnostic blood test with a poor sensitivity (but better than chance) on a very rare disease. As an oversimplification: for a bound take your population * workup rate * fatality rate due to workup and you have a baseline needless death due to the screening (NB there is basically always a fatality rate). The number you are comparing to is lives saved due to earlier detection. Better than chance means it's strictly more information always. But as policy, you shouldn't do it unless you can be extremely confident that lives saves is much larger than lives lost due to the process. This is a bit counter intuitive, but it is a fundamental issue in a lot of healthcare policy. The real calculations are more complex but in the end it is unavoidably actuarial in nature.
      - kragen 3y ago
        i explained this in https://news.ycombinator.com/item?id=37267690 https://news.ycombinator.com/item?id=37267690 except that i suggested using a better measure than crude fatality rate, such as daly this is not a global optimization problem; it's a local optimization problem. one person is deciding whether or not to spend their own money on an mri, or a blood test or whatever, on themself. they are the ones in the best position to do that, and for very-low-risk tests like mris it is very rare that the optimal decision is for a rich person not to get them another nuance is that you don't have to be extremely confident that the mri or biopsy or whatever will increase your expected daly or qaly or whatever; in the cases where you're not extremely confident, it's because it doesn't matter much either way, because you're weighing two extremely small risks against each other. if you make the wrong decision and lose (in expectation, risk-adjusted) a hundredth of a qaly to a blood test or an extremely unlikely cancer, it wasn't a terrible decision, just a small mistake (even if that small mistake kills you in three months) the cases where the decision matters, it's easy to get enough information to be extremely confident
        ska 3y ago
        Well I did say the actual calculations would be (and are) more complicated. And as I said, short of availability constraints, the MRI itself isn't an issue, it's the follow up. Ignoring the fact that in the real world due to constraints this isn't really a local optimization, if we assume infinite availability you still have a problem that low sensitivity tests lead to excess unnecessary work up risks. Your assertion that it is always easy to get good information leading to correct choices here is just incorrect and probably naive. The trade offs you are talking about are very well known and have been studied by professionals for decades; none of them will claim it easy - for good reasons. Note I'm not appealing to authority here. Many people can educate themselves to the degree that in a narrow area of their own healthcare they are as or more knowledgable than the average professional. However, this is not at all easy, and will require a ton of work. The cost benefit for a lot of screening etc. just isn't there; for a particularly symptomatic disease it may well be.

by ska 3y ago

kragen 3y ago

that's just because the radiologists' standard for 'could justify work up' are too low

ska 3y ago
Or it's because the problem is genuinely hard. See above ('imperfect sensitivity')... the same problem exists in e.g. blood tests. I'm no radiologist but I've seen enough of this done that I'd lean that way. Especially if you consider realistic bounds on time and additional information.
- kragen 3y ago
  yes, of course the problem is genuinely hard, but having less information about your body makes it harder, not easier
  - ska 3y ago
    In the abstract more information is always better. In practical healthcare with real constraints, sometimes it makes things worse globally for reason above. Think about say a diagnostic blood test with a poor sensitivity (but better than chance) on a very rare disease. As an oversimplification: for a bound take your population * workup rate * fatality rate due to workup and you have a baseline needless death due to the screening (NB there is basically always a fatality rate). The number you are comparing to is lives saved due to earlier detection. Better than chance means it's strictly more information always. But as policy, you shouldn't do it unless you can be extremely confident that lives saves is much larger than lives lost due to the process. This is a bit counter intuitive, but it is a fundamental issue in a lot of healthcare policy. The real calculations are more complex but in the end it is unavoidably actuarial in nature.
    - kragen 3y ago
      i explained this in https://news.ycombinator.com/item?id=37267690 https://news.ycombinator.com/item?id=37267690 except that i suggested using a better measure than crude fatality rate, such as daly this is not a global optimization problem; it's a local optimization problem. one person is deciding whether or not to spend their own money on an mri, or a blood test or whatever, on themself. they are the ones in the best position to do that, and for very-low-risk tests like mris it is very rare that the optimal decision is for a rich person not to get them another nuance is that you don't have to be extremely confident that the mri or biopsy or whatever will increase your expected daly or qaly or whatever; in the cases where you're not extremely confident, it's because it doesn't matter much either way, because you're weighing two extremely small risks against each other. if you make the wrong decision and lose (in expectation, risk-adjusted) a hundredth of a qaly to a blood test or an extremely unlikely cancer, it wasn't a terrible decision, just a small mistake (even if that small mistake kills you in three months) the cases where the decision matters, it's easy to get enough information to be extremely confident
      - ska 3y ago
        Well I did say the actual calculations would be (and are) more complicated. And as I said, short of availability constraints, the MRI itself isn't an issue, it's the follow up. Ignoring the fact that in the real world due to constraints this isn't really a local optimization, if we assume infinite availability you still have a problem that low sensitivity tests lead to excess unnecessary work up risks. Your assertion that it is always easy to get good information leading to correct choices here is just incorrect and probably naive. The trade offs you are talking about are very well known and have been studied by professionals for decades; none of them will claim it easy - for good reasons. Note I'm not appealing to authority here. Many people can educate themselves to the degree that in a narrow area of their own healthcare they are as or more knowledgable than the average professional. However, this is not at all easy, and will require a ton of work. The cost benefit for a lot of screening etc. just isn't there; for a particularly symptomatic disease it may well be.