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Potential false-positive rate among the 'asymptomatic infected individuals'

ncbi.nlm.nih.gov

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Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#61

Post by lbj »

glofish wrote: post #14
mempko wrote: post #12

Earlier quoted context omitted.

Or think about it this way, this means as a percentage of real people infected, the mortality rate of COVID-19 is higher than thought. This false-positive rate means that the number of real cases is lower than reported and therefore mortality rate is higher. In other words, COVID-19 is more dangerous than thought if you catch it. Then again, I'm sure the actual cases dwarfs those reported since not everyone has been…

Mortality is almost always much lower than the initially reported and observed numbers. There could be many more people that never even get to the testing phase.

The mortality rate in Denmark is still a flat 0.0

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#62

Post by AnthonyMouse »

usrusr wrote: post #46
andrewseanryan wrote: post #29

Earlier quoted context omitted.

Would I be correct with the following: If the false positive rate is higher than the expected rate of disease in a given community, then the majority of positive tests will be false positives. Does this relate to COVID in any way? Since the rates among affected communities seem to be growing rapidly. Would appreciate your thoughts.

Looking at growth rate with false positives is a bit of a mindbender: if you limit your testing to the potential contacts of a positive (false or not), you could get a "false R0" virtual epidemic from testing alone, if and only if you test more contacts per positive than 1/false positive rate. Unfortunately, actual hospitalizations and and deaths rule out a virtual epidemic so this is not a hope to cling to.

> Unfortunately, actual hospitalizations and and deaths rule out a virtual epidemic so this is not a hope to cling to.

Not necessarily. In theory all the deaths could have some other cause, i.e. some fraction of people with a different underlying fatal condition had false positive tests for this coronavirus and then died of the other condition.

That's probably not what's happening, but it's theoretically possible. (It's also probable that some of the reported deaths are that, but who knows what percentage.)

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#63

Post by wool_gather »

peterwoerner wrote: post #22
ses1984 wrote: post #19

Earlier quoted context omitted.

>If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. Can you elaborate on this a little more...?

This is a classic result in Bayesian theory. Here is someone else explaining it. https://betterexplained.com/articles/an-intuitive-and-short-...

That is a really excellent explanation. Thanks for sharing it.

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#64

Post by jbay808 »

ses1984 wrote: post #19
cultus wrote: post #18

One fallacy that seems universal with healthcare folks is they think the false positive rate is the chance that a given positive result is erroneous. If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. This is why prior probabilities need to be taken into account in making decisions.

>If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. Can you elaborate on this a little more...?

In the extreme case, imagine that nobody actually has the condition. Then every positive result is a false positive. The thing we call the "false positive" rate might still be only 1% though; that just means the test is correctly identifying 99% of people as negative and 1%, falsely, as positive.

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#66

Post by lbj »

jmartinpetersen wrote: post #16
lbj wrote: post #9

In Denmark we increased our testing 10-fold and found 300% more people infected. Our response to that increase has been to shut down the country completely for 2 weeks and expand our governments right to act: Forced entry into private property, forced isolation and treatment, forced testing. If this is all because of an error in the test kit I'm going to be super ticked off.

This is somewhat misleading information. First, the country has NOT been completely shut down. I went shopping today and bought milk, yeast and flour. We didn't need toilet paper, but the store had plenty. All schools and most of the public sector closes down for two weeks on Monday. Some business (like restaurants, movie theaters and fitness gyms) are closing down on their own accord. But you can - if you will - sti…

You are correct on all points, thanks for letting me know about the changed proposal.

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#67

Post by ses1984 »

Cerium wrote: post #23
ses1984 wrote: post #19

Earlier quoted context omitted.

>If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. Can you elaborate on this a little more...?

If a given test has a 1% chance of returning true, even when the actual result is false, then from a sample of say 1000 tests we would expect at least 10 trues, in addition to any actual true results. If the chance of having the disease in the general population is low (say 1 in a thousand for this example) then we would expect 11 true results in our thousand samples. Of which 91% are incorrect results - false positi…

Does 1% error rate mean it's positive 1% of the time or wrong 1% of the time?

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#68

Post by DuskStar »

ses1984 wrote: post #19
cultus wrote: post #18

One fallacy that seems universal with healthcare folks is they think the false positive rate is the chance that a given positive result is erroneous. If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. This is why prior probabilities need to be taken into account in making decisions.

>If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. Can you elaborate on this a little more...?

As always, there's an XKCD for this: https://xkcd.com/1132/

Basically, imagine that it's a decade from now, and no one in the world has COVID-19 anymore. The test still has a 1% false-positive rate, though - so if you test a few thousand people, a few of them will test positive. Given that setup, every single one of the test positives will be false positives.

The same holds true if there's one infected person and you test 1,000,000.

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#69

Post by 9HZZRfNlpR »

AnthonyMouse wrote: post #54
9HZZRfNlpR wrote: post #44

Earlier quoted context omitted.

How does it relate to universal Healthcare? I'm not an American so maybe I'm missing something.

A "fallacy that seems universal with healthcare folks" is not expected to be related to universal healthcare.

Yes, that was rather embarrasing. Sorry about that.

Re: Potential false-positive rate among the 'asymptomatic infected individuals'

#70

Post by eveningcoffee »

mikorym wrote: post #36
cultus wrote: post #18

One fallacy that seems universal with healthcare folks is they think the false positive rate is the chance that a given positive result is erroneous. If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. This is why prior probabilities need to be taken into account in making decisions.

I appreciate all the answers that point out Bayes's theorem. One thing to add is that in contrast to the usual classroom Bayes the "occurrence in the general population" is very much a variable rather than a constant. For example, Germany's low death rate can be a side effect of the false positive issue in the paper. In fact, the stark difference between Italy and Germany would provide support to the paper's conclusi…

There can be other explanation for this difference http://www.savespain.eu/italy-vs-germany because there is huge disparity between Italy and Germany infected population demographic.

My hypothesis is that this comes from bigger inter-generation connections in Italy.

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