4 ms·

With a 50% false positive rate, most of your positives are false positive. You might as well just tell everyone who asks for a test that they're infected.

by beojan 7y ago

dependsontheq 7y ago
From a public health perspective ... this could be a brilliant solution.
- mnd999 7y ago
  Until they all decide that they’re immune and don’t need to worry about it anymore.
  - fortran77 7y ago
    Exactly. I think many people, upon learning they're positive by asymptomatic would (maybe) wait a week to make sure they don't feel ill, and then go out into the world, potentially spreading the virus with abandon because they're among the group that doesn't get ill from it.
- lozenge 7y ago
  Until Fox News or the governor of West Virginia blows the illusion away.
  - ramblerman 7y ago
    Huh, I'm lost in this thread. So, We lie to people and tell em they are infected. And then we are angry that FOX or the governor of WV are going to expose our scam? What did I miss...
    - beojan 7y ago
      You could tell them the test came back positive. That's not really a lie.
- dguest 7y ago
  You should account for ignorance in public health policy, but you shouldn't rely on it. Having more false positives than true positives only works if the people taking the test either don't understand statistics or don't know the test accuracy. I for one would probably ignore a positive result if I thought my chances of true positive were 0.001 and my chances of a false positive were 0.5.
- gpderetta 7y ago
  That's a great way to lose any remaining confidence the population might have on the establishment. It is also probably unethical so I doubt any doctor would go with it.
  - mistermann 7y ago
    It's a perfectly valid concern, but I don't think it needs to turn out the way your fear. How about we try this: when reporting "facts", how about we try noting that there is uncertainty involved? I know the average Joe and Jane public aren't intellectuals, and it is often how stupid people can be, but on the other hand I think it is also fair to say that we underestimate people. I think we should at least consider trying this (noting uncertainty in reporting) - it's times like this where we need more ideas and more thinking, not less.
deleted 7y ago
[deleted]
ptero 7y ago
There is a big system-level difference: with 50% false positive, half of the population goes back to living regular lives. False positives stay home, and go to a hospital only if they need a ventialtor (which very few will need since they are not actually sick)
- notyourday 7y ago
  If you can't breath you go to the hospital regardless of it being COVID-19.
- owl57 7y ago
  There are 50% false positive, and there are some false negative. And some more not exactly false negative, but simply got sick after the test. And you tell them: we tested everyone, all negatives can just resume normal life. What could go wrong?
radu_floricica 7y ago
50% is a bit of information. You can repeat the test - even if you consider that some contamination survives repeated tests, if you even get half a bit from subsequent tests you can easily get to eliminate quite a bit of population.
- astrophysician 7y ago
  Yea but not nearly enough of the population for this to meaningfully change the response, and now you’ve made the testing results completely meaningless so that we can’t track the disease. Maybe it’s not intuitive to people but we are actually worse off with a test that’s this bad than just the extremely limited testing that’s being done now
  - radu_floricica 7y ago
    I admit it's not intuitive. Tell me more? I'm assuming there's high false positive rate. If the test has even moderate false negative, then yes it's worse than useless.
    - astrophysician 7y ago
      High false positive rate (I’m talking like more than 1%) means (1) you are overwhelmingly unlikely to actually have the disease even if your test comes back positive but you don’t have obvious symptoms (2) the pool of people testing positive is completely dominated by false positives. The fraction of people testing positive that will actually have the disease would be very small, so you lose the epidemiological benefit of the test (now you can’t actually track the disease well). So — test is useless for people like you and me who don’t have symptoms or a strong prior probability of having covid BEFORE the test, because even a positive result is overwhelmingly more likely to be wrong, AND now the epidemiologists trying to actually track the disease are instead overwhelmed with false positives so the true signal disappears. It’s bad all around. You could imagine using this as a screening tool, but the false positive rate has to be small enough for that purpose as well (like, less than one percent).
Symmetry 7y ago
Having 50% of all tests come back positive is way too high and makes the test basically useless. But having 50% or more of positive tests being false positives is probably the right tradeoff, though you probably want to re-test people who don't show symptoms.

With a 50% false positive rate, most of your positives are false positive. You might as well just tell everyone who asks for a test that they're infected.

by beojan 7y ago

With a 50% false positive rate, most of your positives are false positive. You might as well just tell everyone who asks for a test that they're infected.

dependsontheq 7y ago

From a public health perspective ... this could be a brilliant solution.

mnd999 7y ago
Until they all decide that they’re immune and don’t need to worry about it anymore.
- fortran77 7y ago
  Exactly. I think many people, upon learning they're positive by asymptomatic would (maybe) wait a week to make sure they don't feel ill, and then go out into the world, potentially spreading the virus with abandon because they're among the group that doesn't get ill from it.
lozenge 7y ago
Until Fox News or the governor of West Virginia blows the illusion away.
- ramblerman 7y ago
  Huh, I'm lost in this thread. So, We lie to people and tell em they are infected. And then we are angry that FOX or the governor of WV are going to expose our scam? What did I miss...
  - beojan 7y ago
    You could tell them the test came back positive. That's not really a lie.
dguest 7y ago
You should account for ignorance in public health policy, but you shouldn't rely on it. Having more false positives than true positives only works if the people taking the test either don't understand statistics or don't know the test accuracy. I for one would probably ignore a positive result if I thought my chances of true positive were 0.001 and my chances of a false positive were 0.5.
gpderetta 7y ago
That's a great way to lose any remaining confidence the population might have on the establishment. It is also probably unethical so I doubt any doctor would go with it.
- mistermann 7y ago
  It's a perfectly valid concern, but I don't think it needs to turn out the way your fear. How about we try this: when reporting "facts", how about we try noting that there is uncertainty involved? I know the average Joe and Jane public aren't intellectuals, and it is often how stupid people can be, but on the other hand I think it is also fair to say that we underestimate people. I think we should at least consider trying this (noting uncertainty in reporting) - it's times like this where we need more ideas and more thinking, not less.

deleted 7y ago

[deleted]

ptero 7y ago

There is a big system-level difference: with 50% false positive, half of the population goes back to living regular lives. False positives stay home, and go to a hospital only if they need a ventialtor (which very few will need since they are not actually sick)

notyourday 7y ago
If you can't breath you go to the hospital regardless of it being COVID-19.
owl57 7y ago
There are 50% false positive, and there are some false negative. And some more not exactly false negative, but simply got sick after the test. And you tell them: we tested everyone, all negatives can just resume normal life. What could go wrong?

radu_floricica 7y ago

50% is a bit of information. You can repeat the test - even if you consider that some contamination survives repeated tests, if you even get half a bit from subsequent tests you can easily get to eliminate quite a bit of population.

astrophysician 7y ago
Yea but not nearly enough of the population for this to meaningfully change the response, and now you’ve made the testing results completely meaningless so that we can’t track the disease. Maybe it’s not intuitive to people but we are actually worse off with a test that’s this bad than just the extremely limited testing that’s being done now
- radu_floricica 7y ago
  I admit it's not intuitive. Tell me more? I'm assuming there's high false positive rate. If the test has even moderate false negative, then yes it's worse than useless.
  - astrophysician 7y ago
    High false positive rate (I’m talking like more than 1%) means (1) you are overwhelmingly unlikely to actually have the disease even if your test comes back positive but you don’t have obvious symptoms (2) the pool of people testing positive is completely dominated by false positives. The fraction of people testing positive that will actually have the disease would be very small, so you lose the epidemiological benefit of the test (now you can’t actually track the disease well). So — test is useless for people like you and me who don’t have symptoms or a strong prior probability of having covid BEFORE the test, because even a positive result is overwhelmingly more likely to be wrong, AND now the epidemiologists trying to actually track the disease are instead overwhelmed with false positives so the true signal disappears. It’s bad all around. You could imagine using this as a screening tool, but the false positive rate has to be small enough for that purpose as well (like, less than one percent).

Symmetry 7y ago

Having 50% of all tests come back positive is way too high and makes the test basically useless. But having 50% or more of positive tests being false positives is probably the right tradeoff, though you probably want to re-test people who don't show symptoms.