41–50 of 149 posts
Me before reading: "this study, like ~every study, will detect no effect on all-cause mortality because that needs a crazy big sample size" After reading: "this study, like ~every study, detected no effect on all-cause mortality because that needs a crazy big sample size" A three-year study where one group magically had zero car crashes would need a sample size of 5,000,000 to detect a difference in all-cause mortali…
Earlier quoted context omitted.
Life expectancy is really only one dimension of "health," and it's probably the most shallow dimension. If I'm quadriplegic and confined to a ventilator but I live to 80, that's the same in this metric as if I'm not paralyzed and able to breathe on my own until I die. What if some people in the group that didn't get screening had fewer high-quality years? It might simply be that the last 5 years of life for people wh…
> Life expectancy is really only one dimension of "health," and it's probably the most shallow dimension. If I'm quadriplegic and confined to a ventilator but I live to 80, that's the same in this metric as if I'm not paralyzed and able to breathe on my own until I die. Claiming that there are missing elements that could possibly turn the equation in favor of screening is cause for further research and analysis. You…
Earlier quoted context omitted.
The paper [1] is more well written and clear than the CNN article. They were comparing the aggregate life expectancies of people who went through regular screenings vs those who did not, and there was near zero difference except for colorectal screenings where the difference was about 4 months of difference. The paper is indeed presenting strong evidence that regular screenings have minimal value. [1] - https://jaman…
> except for colorectal screenings where the difference was about 4 months of difference That sounds, uh, significant. So to clarify, does that mean people gain 4 months on average by getting this screening? Those who get the cancer gain years, and those that don't gain 0, so the average is 4 months?
If we take your theory at face value, on average the screened people would have an 8 month increase.
> But experts say this doesn’t mean you should cancel that colonoscopy or mammogram appointment. That can only be that these experts disagree with the study, because if it were properly conducted such that its findings are true, then in fact its conclusions do add up to skipping colonoscopies and mammograms. The study is saying that the diagnostic procedures have no effect on outcome. You should not waste time on pro…
The article dismisses a population-wide life expectancy increase of 4 months from one of the screens. If that's your bar, then most preventative screening is probably not worthwhile.
It's pretty dishonest to be confusing the effect of screening by counting unscreened individuals.
It's like claiming that seat belts don't work by looking only at fatality figures that don't inform to what extent seatbelts were worn.
Earlier quoted context omitted.
There's an amazing mathematical paradox, maybe even better than the birthday paradox, related to screening for rare diseases, that dramatically changes the formula. Imagine there's some terrible disease affects 1 in 1 million people. And there's a test that's 99% accurate. You go get screened for the disease, and it comes up positive. Oh no! What are the chances that it was a false positive? Intuition would tell you…
Oh no! But what if we run the test a third time?
An excellent episode of EconTalk came out today on this very subject: Open: https://simplecast.econtalk.org/episodes/vinay-prasad-on-can... Apple: https://podcasts.apple.com/us/podcast/econtalk/id135066958?i... Highly recommend the episode and show. The gist is that cancer is only 4% of deaths, and screening only reduces those 4% by 20% (so it does not help whatsoever 80% of cancers). But there is a lot more to the e…
This is the pertinent quote: > “Cancer screening was never really designed to increase longevity. Screenings are really designed to decrease premature deaths from cancer.” Explained another way, Dahut said, if a person’s life expectancy at birth was 80, a cancer screening may prevent their premature death at 65, but it wouldn’t necessarily mean they’d live to be 90 instead of the predicted 80. Personally I think this…
Yes, life expectancy should count premature deaths
Saying it "doesn't extend live" goes against that, because it absolutely does increase life expectancy
Science communication is bad
I am skeptical of the implied lesson of this analysis—and it is a meta-analysis of other research, not an original study. Just take as given that the analysis is correct, and screening for rare Disease A on net has no effect on life expectancy. Almost no one actually gets Disease A, but everyone is screened for it, and that has some diffuse cost to life expectancy: Screen enough people enough times and someone will d…
There's an amazing mathematical paradox, maybe even better than the birthday paradox, related to screening for rare diseases, that dramatically changes the formula. Imagine there's some terrible disease affects 1 in 1 million people. And there's a test that's 99% accurate. You go get screened for the disease, and it comes up positive. Oh no! What are the chances that it was a false positive? Intuition would tell you…
Imagine you test early and often for a condition in country A much more often than country B which waits until some more late stage easier to detect symptoms occur. Now compare survivor rates. Much higher in country A! We should clearly also be testing in country B, right?
Depends. If the condition is something that doesn’t often actually kill and typically remains at a non lethal but detectable state then all you might have done is treat a lot of extra non fatal conditions that usually only is detected in country B once it evolves to a more advanced and dangerous state. You may have put many people in country A through an unnecessary, expensive, and frightening treatment regime.
The point is that these things are complex and need thorough analysis.