Study of 160k men finds no all-cause mortality benefit from prostate screening • Hacker News Board

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#21

Post by bermanoid » Mon, Mar 19, 2012, 4:46 AM UTC

Sniffnoy wrote: post #19

bermanoid wrote: post #18

Earlier quoted context omitted.

From the link you posted: "last month, the American Cancer Society urged more caution in using the test" It's a very sad state of affairs when a test that unambiguously offers some statistical utility (speaking as a Bayesian, any test is useful if we do the right things with the results, this is quite literally a provable theorem of decision theory) is potentially problematic because we aren't properly evaluating wha…

Unless taking the test has a cost in and of itself -- such as if it requires surgery, so that the risk of something going wrong during testing might outweigh the information gained if the condition being tested for is rare.

Yup, definitely, I should have made that more clear than it was (I did mention "after discounting for the cost of the test", but it wasn't as obvious as it should have been). Test costs have to be weighed against benefits, but that whole process involves a lot more statistical sophistication than is typically applied in practiced medicine. Researchers are slightly better, though it's fairly common even for them to make hideous statistical mistakes, which is a real problem in the field.

IMO, if pre-med requirements included a bit more statistics and a bit less biology, we'd all be better off...

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#22

Post by rwallace » Mon, Mar 19, 2012, 7:14 AM UTC

Alex3917 wrote: post #10

Thank you for phrasing this in terms of all-cause mortality. If only every academic study (and submission) used this as a metric, the world would be a vastly better place.

Well, not quite. All-cause mortality is not the appropriate metric for treatments targeted at people already known to be sick. Where it is appropriate is the case of blanket programs, like cancer screening, intended to be applied to the population in general.

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#23

Post by coldarchon » Mon, Mar 19, 2012, 7:46 AM UTC

Or to make it short, when the time has come - it has come. No matter which part of you fails, it is not the reason ..

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#24

Post by carbocation » Mon, Mar 19, 2012, 9:04 AM UTC

bermanoid wrote: post #20

bryanlarsen wrote: post #9

Earlier quoted context omitted.

Somebody correct me if I'm wrong, but here's the way I understand it. One of the major problems with PSA-based screening is false-positives. Getting a false-positive result for cancer could certainly increase your risk of an early death. Cancer treatments put a lot of stress on you physically, and the diagnoses could also cause a lot of mental/emotional stress. Stress of either kind reduces life expectancy.

False positive rates should be understood by the doctors that recommend treatments, though. A doctor should be able to accurately tell a patient what the chance is that they suffer from a disease based on a positive result from a test. Unfortunately, doctors tend to be terribly bad at this - they are generally quite inept at incorporating prior probabilities into the estimates, and assume that (for instance) if a tes…

A classic systems problem. If something is this important, you don't leave it up to the decision of thousands of inhomogenous physicians. You create a system that ensures they don't even get to choose to get it wrong.

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#25

Post by waveman » Mon, Mar 19, 2012, 9:27 AM UTC

fishtoaster wrote: post #3

It looks like this is the 2 year follow up to a previous study. "Analyses after 2 additional years of follow-up consolidated our previous finding that PSA-based screening significantly reduced mortality from prostate cancer but did not affect all-cause mortality. " So, if I follow this correctly, your odds of dying from prostate cancer are still definitely lowered by screening, but your odds of dying overall are not.…

This is so frustrating. In medical studies the word "significant" does not mean what it means in normal English. It refers to the possibility that the effect was due to chance, not to how large, important, or clinically significant the effect is.

The study found no significant difference. This does NOT means the study found there was no difference. What it means is that the study was not large enough or the effect was not large enough to prove that the reduction was real at 95% significance.

In fact the screened men died at a LOWER rate. It was just that the effect could possibly have been due to chance.

So realistically the report should say "PSA screening probably saves lives but more study is needed to be sure and to determine how large the effect is".

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#26

Post by [deleted] » Mon, Mar 19, 2012, 9:28 AM UTC

niels_olson wrote: post #16

Alex3917 wrote: post #10

Thank you for phrasing this in terms of all-cause mortality. If only every academic study (and submission) used this as a metric, the world would be a vastly better place.

I doubt it. If you relied on all-cause mortality for every study, you'd never get out of phase I trials.

[deleted]

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#27

Post by waveman » Mon, Mar 19, 2012, 9:30 AM UTC

scythe wrote: post #15

fishtoaster wrote: post #3

It looks like this is the 2 year follow up to a previous study. "Analyses after 2 additional years of follow-up consolidated our previous finding that PSA-based screening significantly reduced mortality from prostate cancer but did not affect all-cause mortality. " So, if I follow this correctly, your odds of dying from prostate cancer are still definitely lowered by screening, but your odds of dying overall are not.…

It probably just means prostate cancer represents a tiny portion of mortality, so even a significant difference appears tiny and within the bounds of error. Remember, the finding is not "no difference" but "failed to find a difference". Statistics does not ever prove "no difference".

Actually not even that. The study found a difference but the effect was not large enough or the study was too small to prove that the effect could not possibly have been due to chance.

Time and time again we get people who should know better equating "no significant difference found" with "found that there was no difference".

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#28

Post by waveman » Mon, Mar 19, 2012, 9:38 AM UTC

Actually there was a reduction in all-cause mortality. It's just that the study's design was such that the reduction could possibly have been due to chance. This is not at all the same thing as "finding no ... benefit".

This lack of statistical significance is probably mainly due to the small size of the study (160 men).

Note that the reduction in death rates from prostate cancer was large in practical terms and (statistically) significant.

Prostate cancer kills a minority of men. Take this fact, add in the fact the study was small, and then throw in all other causes of death (which vary randomly) then it is not at all surprising that the result was not statistically significant. This is mainly due to a small study and noise from other causes of death.

I for one am going to keep having my PSA tests.

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#29

Post by waveman » Mon, Mar 19, 2012, 9:40 AM UTC

waveman wrote: post #28

Actually there was a reduction in all-cause mortality. It's just that the study's design was such that the reduction could possibly have been due to chance. This is not at all the same thing as "finding no ... benefit". This lack of statistical significance is probably mainly due to the small size of the study (160 men). Note that the reduction in death rates from prostate cancer was large in practical terms and (sta…

Having said that, the state of Prostate Cancer treatment and the lack of research into Prostate Cancer is a disgrace.

Prostate cancer kills similar numbers to breast cancer yet gets half the research funding. Thank goodness we live in a patriarchal society or the ratio would be even more in women's favor.

I have watched two male relatives die of Prostate Cancer and it is not a good way to go.

Re: Study of 160k men finds no all-cause mortality benefit from prostate screening

#30

Post by Shaanie » Mon, Mar 19, 2012, 10:55 AM UTC

waveman wrote: post #28

Actually there was a reduction in all-cause mortality. It's just that the study's design was such that the reduction could possibly have been due to chance. This is not at all the same thing as "finding no ... benefit". This lack of statistical significance is probably mainly due to the small size of the study (160 men). Note that the reduction in death rates from prostate cancer was large in practical terms and (sta…

160k means 160.000 men. That's a pretty huge sample size. Not statistically significant means we cannot with at least a 95% certainty say that the treatment helps.