6 ms·
> This is absurd. It is not, and the issues are central to both statistics and medicine. 1) Medical tests have four quadrants--not 2. The accurate quadrants
by bsder 5y ago
> This is absurd.
It is not, and the issues are central to both statistics and medicine.
1) Medical tests have four quadrants--not 2. The accurate quadrants are "positive test--positive diagnosis" and "negative test--negative diagnosis". The problem quadrants are "positive test--negative diagnosis" and "negative test--positive diagnosis".
A positive test with a negative diagnosis can cause issues like they do for mammograms. The problem is that the followup procedures have a non-zero probability of killing the patient. Biopsies can result in infections. Anxiety from a positive test can cause heart attacks and strokes. If your test is only 99% accurate, then 1% of people being tested are incurring those risks when they don't have to. If you are testing a lot of people and the disease is relatively rare, you may kill more people with false positives than the disease itself.
A negative test with a positive diagnosis is problematic because people will tend to blow off other signs since "the test was negative". This can delay lifesaving treatment.
Finally, optimizing one of those quadrants generally occurs at the expense of another. So, which should a test prefer?
2) The body often clears a lot of diseases. Lumps that could be cancerous often disappear. Swellings come and go. Viruses do more and varied damage than we originally thought. The body repairs itself and reversion to the mean is a thing.
3) Diseases may not even be that problematic. Sure, aggressive prostate cancer is an issue. However, practically every single man will eventually get prostate cancer. Most men die of something else before prostate cancer is an issue. Is it worth risking becoming incontinent or impotent from a prostate cancer treatment?
4) Will the positive test even lead to a correct request for treatment? People demand antibiotics for viral infections all the time. My body never gets rid of strep throat, so I will force my doctor to give me a quick strep test when I have a persistent sore throat. The first time I did this my doctor was literally stunned when I simply thanked him and got ready to walk out since the test came back negative. Everyone else will demand antibiotics even if the test is negative.
- tomohawk 5y agoI wonder if some of this could be mitigated with a sort of double blind take home test. You take the test, but you do not know what it is screening for, or what the results mean. It tests for N things which can be economically packaged. The results can then be used to produce a recommendation for additional consultation with a doctor.
- light_hue_1 5y ago> 1) Medical tests have four quadrants--not 2. The accurate quadrants are "positive test--positive diagnosis" and "negative test--negative diagnosis". The problem quadrants are "positive test--negative diagnosis" and "negative test--positive diagnosis". The solution to false positives is not "let's not test and bury our heads in the sand". The solution to false positives is to test a lot more to monitor the progression of disease. > Biopsies can result in infections ... If you are testing a lot of people and the disease is relatively rare, you may kill more people with false positives than the disease itself This is junk science. People troll through records looking for correlations and publish when they find them. Many prospective studies show that biopsies don't increase mortality rates. > A negative test with a positive diagnosis is problematic because people will tend to blow off other signs since "the test was negative". This can delay lifesaving treatment. If you have symptoms you will be given a test anyway. So you need to deal with base rates, false positives, etc, regardless. > 2) The body often clears a lot of diseases. Lumps that could be cancerous often disappear. Swellings come and go. Viruses do more and varied damage than we originally thought. The body repairs itself and reversion to the mean is a thing. So the solution is to monitor them constantly. > 3) Diseases may not even be that problematic. Sure, aggressive prostate cancer is an issue. However, practically every single man will eventually get prostate cancer. Most men die of something else before prostate cancer is an issue. Is it worth risking becoming incontinent or impotent from a prostate cancer treatment? Yup. I said that above. The problem is that without universal screening we don't know anything about which cancers are going to be a problem and which are not. And we don't have data to target drugs and interventions. The solution is to have universal screening and regular followups, then use the data to narrow down who needs treatment. > 4) Will the positive test even lead to a correct request for treatment? People demand antibiotics for viral infections all the time. My body never gets rid of strep throat, so I will force my doctor to give me a quick strep test when I have a persistent sore throat. The first time I did this my doctor was literally stunned when I simply thanked him and got ready to walk out since the test came back negative. Everyone else will demand antibiotics even if the test is negative. You can demand whatever you want. What does that have to do with anything?