3 ms·

There's not confusion. The study did an intention-to-treat analysis, which failed to find a significant result. "Intention to treat" here means that you count

by timr 4y ago

There's not confusion. The study did an intention-to-treat analysis, which failed to find a significant result. "Intention to treat" here means that you count everyone in the group that got an invitation to get a colonoscopy, regardless of whether or not they actually did it. Though this sounds counterintuitive, it's the "gold standard" because, if you don't do this, you leave yourself open to bias -- maybe the people who seek out colonoscopy have some symptom, family history or other reason that leads them to seek out treatment. Maybe the people who get a test get more treatment, and that treatment is harmful in the marginal case. Or just as importantly: maybe the people who don't have the time/inclination to do one would be better served by an alternative test. Everyone (including GP) is fixating on the magnitude of the primary outcome and squabbling about whether or not colonoscopies help people. But I think the more interesting aspect of this study is that it shows that the genetic tests probably aren't inferior to the invasive, painful, time-consuming rectal exam. If that's true, it's great news!

2devnull 4y ago
The important part of your post, “If that’s true…” Is it true, or not?
- timr 4y ago
  To the extent that we can assess it by this single study, yes. There is no answer to the question you're asking. You're seeking absolute certainty where none can be had. We only know what we know as far as we know it. Always and everywhere.
dahart 4y ago
> Though this sounds counterintuitive, it’s the “gold standard” because, if you don’t do this, you leave yourself open to bias Isn’t there just as much chance for bias if the treatment is voluntary? Maybe the people who are more likely to have health issues are less likely to treat them. I think there is a valid question about how effective a colonoscopy is given that you get one, and a separate valid question about how effective telling people to get colonoscopies is. According to the article, this paper answer the second question strongly via “gold standard”, and the first question less strongly via secondary analysis. Part of the reason it’s counterintuitive here is the title of the article is “effect of colonoscopy screening”, not “effect of a doctor’s invitation to have a colonoscopy screening”. The title more than suggests that we’re comparing the outcomes of actually having the screening to not having one. > maybe the people who don’t have the time/inclination to do one would be better served by an alternative test. I see what you’re saying - the overall effectiveness of our current system may be low because of a low rate of voluntary adoption of the colonoscopy is low, and even a lower accuracy screen could be more effective if more people opt in. One problem with drawing a conclusion this way is it ignores the possibility for dramatic changes in either opinion or in procedure of colonoscopies. What if we had the tech to do the colonoscopy at home in private? Would that change the voluntary rate of testing dramatically?
- timr 4y ago
  > Isn’t there just as much chance for bias if the treatment is voluntary? I'm not quite sure what you're asking here. If you're wondering if voluntary opt-out of colonoscopy carries risk of bias, then I'll say the following: it's an intervention that is painful, intrusive and time consuming. No reasonable person would get one absent demonstrated benefit. Pick a thing where people are reasonably likely to do it as default behavior (eating chocolate, say), and the intervention is to abstain from doing the thing, then you'd be right to ask that question. I imagine people who voluntarily abstain from chocolate are pretty different in substantial ways than people who have to be coerced to do so. But people who don't get a colonoscopy when not pestered to do so are just...normal. > I see what you’re saying - the overall effectiveness of our current system may be low because of a low rate of voluntary adoption of the colonoscopy is low, and even a lower accuracy screen could be more effective if more people opt in. Not quite. I'm saying that this study did the fairest possible test for effectiveness of colonoscopies, and the effect sizes they found were on par with the genetic tests (to be clear: they didn't actually make this comparison in the RCT; I'm extrapolating from other studies.) The evidence presented here is not that the genetic tests are a "lower accuracy screen", it's that colonoscopies are likely not better than genetic tests. That's very different.
  - jdeibele 4y ago
    My father died of colon cancer at age 67. I've been getting screened every 5 years, first by sigmoidoscopy and the last couple of times with the full colonoscopy. With a sigmoidoscopy you're awake and the doctor will show you what they're looking at. I guess that's intrusive but it certainly wasn't painful. With colonoscopy, you're under anesthesia. It was probably intrusive but since I wasn't conscious, I didn't care. There was no pain when I regained consciousness. I'd rather do a stool sample by mail or dropping it off at the clinic if it has the same results as the colonoscopy. There's always a risk with general anesthesia. I don't know if my case is the norm and yours is the exception. I tend to think it is. My dad missed spending time with his grandchildren and it's possible he'd still be around if he'd been examined. So get that colonoscopy.
    - 4y ago

by timr 4y ago

2devnull 4y ago

The important part of your post, “If that’s true…” Is it true, or not?

timr 4y ago
To the extent that we can assess it by this single study, yes. There is no answer to the question you're asking. You're seeking absolute certainty where none can be had. We only know what we know as far as we know it. Always and everywhere.

dahart 4y ago

> Though this sounds counterintuitive, it’s the “gold standard” because, if you don’t do this, you leave yourself open to bias Isn’t there just as much chance for bias if the treatment is voluntary? Maybe the people who are more likely to have health issues are less likely to treat them. I think there is a valid question about how effective a colonoscopy is given that you get one, and a separate valid question about how effective telling people to get colonoscopies is. According to the article, this paper answer the second question strongly via “gold standard”, and the first question less strongly via secondary analysis. Part of the reason it’s counterintuitive here is the title of the article is “effect of colonoscopy screening”, not “effect of a doctor’s invitation to have a colonoscopy screening”. The title more than suggests that we’re comparing the outcomes of actually having the screening to not having one. > maybe the people who don’t have the time/inclination to do one would be better served by an alternative test. I see what you’re saying - the overall effectiveness of our current system may be low because of a low rate of voluntary adoption of the colonoscopy is low, and even a lower accuracy screen could be more effective if more people opt in. One problem with drawing a conclusion this way is it ignores the possibility for dramatic changes in either opinion or in procedure of colonoscopies. What if we had the tech to do the colonoscopy at home in private? Would that change the voluntary rate of testing dramatically?

timr 4y ago
> Isn’t there just as much chance for bias if the treatment is voluntary? I'm not quite sure what you're asking here. If you're wondering if voluntary opt-out of colonoscopy carries risk of bias, then I'll say the following: it's an intervention that is painful, intrusive and time consuming. No reasonable person would get one absent demonstrated benefit. Pick a thing where people are reasonably likely to do it as default behavior (eating chocolate, say), and the intervention is to abstain from doing the thing, then you'd be right to ask that question. I imagine people who voluntarily abstain from chocolate are pretty different in substantial ways than people who have to be coerced to do so. But people who don't get a colonoscopy when not pestered to do so are just...normal. > I see what you’re saying - the overall effectiveness of our current system may be low because of a low rate of voluntary adoption of the colonoscopy is low, and even a lower accuracy screen could be more effective if more people opt in. Not quite. I'm saying that this study did the fairest possible test for effectiveness of colonoscopies, and the effect sizes they found were on par with the genetic tests (to be clear: they didn't actually make this comparison in the RCT; I'm extrapolating from other studies.) The evidence presented here is not that the genetic tests are a "lower accuracy screen", it's that colonoscopies are likely not better than genetic tests. That's very different.
- jdeibele 4y ago
  My father died of colon cancer at age 67. I've been getting screened every 5 years, first by sigmoidoscopy and the last couple of times with the full colonoscopy. With a sigmoidoscopy you're awake and the doctor will show you what they're looking at. I guess that's intrusive but it certainly wasn't painful. With colonoscopy, you're under anesthesia. It was probably intrusive but since I wasn't conscious, I didn't care. There was no pain when I regained consciousness. I'd rather do a stool sample by mail or dropping it off at the clinic if it has the same results as the colonoscopy. There's always a risk with general anesthesia. I don't know if my case is the norm and yours is the exception. I tend to think it is. My dad missed spending time with his grandchildren and it's possible he'd still be around if he'd been examined. So get that colonoscopy.
  - 4y ago