7 ms·

> 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 abou

by bryan0 4y ago

> 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. I’m really confused by this data. First of all, are they testing the efficacy of colonoscopy or the efficacy of inviting people to colonoscopy? And then how is the former group’s reduction in deaths 50% and the latter group’s is about 0%?

hannob 4y ago
They're doing an intention to treat analysis, which can be a bit confusing, but statistically makes sense and is the gold standard for clinical trials. You're basicall saying "our randomization at the beginning of the trial is key to avoid biases, so we can't reassign people from the treatment group to the other group, even if they practically don't get the treatment". The reason is if you allow people to switch, your assignment is no longer random. People who avoid the treatment may have different health properties than the ones who don't. In essence, you need your trial to be robust and large enough that a few people not getting the treatment don't matter.
- bryan0 4y ago
  Thanks. That explanation on avoiding selection bias makes sense, but it seems like the study is saying those who choose to get a colonoscopy (whether invited or not) are 50% less likely to die of colon cancer. Also I’m not sure if the article mentioned this, but the data seems to imply that the % of people who opted to get a colonoscopy was similar in the invited and control group.
  - akvadrako 4y ago
    That suggests something strange though – that those who were invited but non-tested were more likely to die of colon cancer than non-invitie non-testers.
    - zerocrates 4y ago
      I suppose that by refusing to get a colonoscopy even when specifically prompted to do so, you're maybe sorting yourself into a more "unhealthy" group than the general population of non-colonoscopy-havers.
      - robertlagrant 4y ago
        That would make the outcome less surprising.
    - bluGill 4y ago
      It would be unethical to refuse to invite someone with a family history of colon cancer. Thus I think it is perfectly reasonable to assume there is something different.
- hef19898 4y ago
  Then the title is wrong, since colonoscopies actually do increase survival rates (everything would have surprised me a lot as someone who was saved by one), but rather that invitations for colonoscopies don't work. No idea why, but maybe people willing to do one go anyway while those unwilling are very unlikely to follow an invitation. Either way, the title is wrong, misleading and very clickbaity.
  - elcomet 4y ago
    What you're saying is not totally correct. If you look only at patients that did get a colonoscopy, you cannot be sure that it is the colonoscopy that helps, or another variable (those people might monitor their health closer). Your assignment is not random any more so you cannot make any causal statement.
JamesBarney 4y ago
The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and more responsible causes you to live longer not the exercise. This could also be true for the colonoscopy, that the more responsible/healthier people in the treatment group are more likely to get the colonoscopy and it's very possible responsibility/healthiness are driving the difference in health outcomes instead of the colonoscopy.
- pbourke 4y ago
  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.
  - deleted 4y ago
    [deleted]
  - JamesBarney 4y ago
    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.
    - 4y ago

by bryan0 4y ago

hannob 4y ago

They're doing an intention to treat analysis, which can be a bit confusing, but statistically makes sense and is the gold standard for clinical trials. You're basicall saying "our randomization at the beginning of the trial is key to avoid biases, so we can't reassign people from the treatment group to the other group, even if they practically don't get the treatment". The reason is if you allow people to switch, your assignment is no longer random. People who avoid the treatment may have different health properties than the ones who don't. In essence, you need your trial to be robust and large enough that a few people not getting the treatment don't matter.

bryan0 4y ago
Thanks. That explanation on avoiding selection bias makes sense, but it seems like the study is saying those who choose to get a colonoscopy (whether invited or not) are 50% less likely to die of colon cancer. Also I’m not sure if the article mentioned this, but the data seems to imply that the % of people who opted to get a colonoscopy was similar in the invited and control group.
- akvadrako 4y ago
  That suggests something strange though – that those who were invited but non-tested were more likely to die of colon cancer than non-invitie non-testers.
  - zerocrates 4y ago
    I suppose that by refusing to get a colonoscopy even when specifically prompted to do so, you're maybe sorting yourself into a more "unhealthy" group than the general population of non-colonoscopy-havers.
    - robertlagrant 4y ago
      That would make the outcome less surprising.
  - bluGill 4y ago
    It would be unethical to refuse to invite someone with a family history of colon cancer. Thus I think it is perfectly reasonable to assume there is something different.
hef19898 4y ago
Then the title is wrong, since colonoscopies actually do increase survival rates (everything would have surprised me a lot as someone who was saved by one), but rather that invitations for colonoscopies don't work. No idea why, but maybe people willing to do one go anyway while those unwilling are very unlikely to follow an invitation. Either way, the title is wrong, misleading and very clickbaity.
- elcomet 4y ago
  What you're saying is not totally correct. If you look only at patients that did get a colonoscopy, you cannot be sure that it is the colonoscopy that helps, or another variable (those people might monitor their health closer). Your assignment is not random any more so you cannot make any causal statement.

JamesBarney 4y ago

The gold standard is the invitation. Imagine a study where you try to get one group of people to exercise, and you leave the other alone as a control group. Imagine you find that everyone who actually does the exercise lives much longer. This might be due to the exercise, or it could be that exercise doesn't work but healthier more responsible people followed through with the exercise. And the being healthier and more responsible causes you to live longer not the exercise. This could also be true for the colonoscopy, that the more responsible/healthier people in the treatment group are more likely to get the colonoscopy and it's very possible responsibility/healthiness are driving the difference in health outcomes instead of the colonoscopy.

pbourke 4y ago
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.
- deleted 4y ago
  [deleted]
- JamesBarney 4y ago
  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.
  - 4y ago