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Hold on, do I understand correctly your comment about the 20% false positive rate? So even if exactly ZERO Americans were experiencing depression, a random samp

Hold on, do I understand correctly your comment about the 20% false positive rate? So even if exactly ZERO Americans were experiencing depression, a random sampling would indicate 20% of Americans are showing signs of depression? And if it's 20% for both tests, that would would correspond to a 36% false positive rate for at least one condition [0]. So the headline that a third of Americans are showing signs of anxiety or depression is consistent with what you'd expect to observe if there was zero (or very small) true prevalence? How does that work out? [0] assuming test results for anxiety and depression are uncorrelated, which seems unlikely. But even if they were 100% correlated, the joint FPR would still be 20%.

nullc 6y ago
https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1861033 https://jamanetwork.com/journals/jamainternalmedicine/fullar... https://blogs.cornell.edu/info2040/2014/11/12/doctors-dont-know-bayes-theorem/ https://blogs.cornell.edu/info2040/2014/11/12/doctors-dont-k...
anbende 6y ago
The situation is a little more complicated as these tests ALSO have a false negative rate. And that false negative rate is also about 20%. As well, the false positive rate is for scores at threshold, which is 3 out of 5. If they score a 4 or a 5, the false positive rate drops dramatically. As well, this isn't an antibody test. Diagnosis is not dichotomous but dimensional. A false positive on depression inventory does not mean the person actually has zero symptoms. It means that their symptoms might actually be mild rather than moderate because of the way they interpreted one or more of the questionnaire items. In general, the way to look at this is that of the people who took the test, 80% of those who scored at threshold would likely receive a diagnosis from a clinician.
- conistonwater 6y ago
  This doesn't address in any way the point being made about false positives leading to overly high estimates of prevalence in the general population, whereas nullc's comment is probably quite close to explaining the issue.
  - legacynl 6y ago
    > This doesn't address in any way the point being made about false positives leading to overly high estimates of prevalence in the general population It does if you are aware of the fact that these tests are never used on its own to diagnose depression/anxiety. The GP or psychologist determines if the client exhibits symptoms of depression, and THEN performs the test, often in combination with other tests that test similar things. Afterwards the results of those tests (as well as the dialogue that's been had with the client), are used in conjunction to determine if a diagnosis is appropriate. I think it's rather arrogant to assume that psychologists/diagnosticians/statisticians are oblivious to the fact that tests have reliability/validity measures. Of course they are aware, that's their job.
    - conistonwater 6y ago
      I'm not sure what you're replying to, I made that exact point upthread and was responding to the disagreement that followed.

nullc 6y ago

https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1861033 https://jamanetwork.com/journals/jamainternalmedicine/fullar... https://blogs.cornell.edu/info2040/2014/11/12/doctors-dont-know-bayes-theorem/ https://blogs.cornell.edu/info2040/2014/11/12/doctors-dont-k...

anbende 6y ago

The situation is a little more complicated as these tests ALSO have a false negative rate. And that false negative rate is also about 20%. As well, the false positive rate is for scores at threshold, which is 3 out of 5. If they score a 4 or a 5, the false positive rate drops dramatically. As well, this isn't an antibody test. Diagnosis is not dichotomous but dimensional. A false positive on depression inventory does not mean the person actually has zero symptoms. It means that their symptoms might actually be mild rather than moderate because of the way they interpreted one or more of the questionnaire items. In general, the way to look at this is that of the people who took the test, 80% of those who scored at threshold would likely receive a diagnosis from a clinician.

conistonwater 6y ago
This doesn't address in any way the point being made about false positives leading to overly high estimates of prevalence in the general population, whereas nullc's comment is probably quite close to explaining the issue.
- legacynl 6y ago
  > This doesn't address in any way the point being made about false positives leading to overly high estimates of prevalence in the general population It does if you are aware of the fact that these tests are never used on its own to diagnose depression/anxiety. The GP or psychologist determines if the client exhibits symptoms of depression, and THEN performs the test, often in combination with other tests that test similar things. Afterwards the results of those tests (as well as the dialogue that's been had with the client), are used in conjunction to determine if a diagnosis is appropriate. I think it's rather arrogant to assume that psychologists/diagnosticians/statisticians are oblivious to the fact that tests have reliability/validity measures. Of course they are aware, that's their job.
  - conistonwater 6y ago
    I'm not sure what you're replying to, I made that exact point upthread and was responding to the disagreement that followed.