Thread: Coronavirus
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Old 25.01.2021, 19:55
leonie leonie is offline
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Re: Coronavirus

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There is random community testing and there is targeted testing of individuals that have symptoms. It seems logical that those who have symptoms are more likely to return a true positive, and not a false positive result.

Here's a BBC article from October that gets into it a bit more
https://www.bbc.com/news/54270373

One paragraph of note, emphasis mine:


It's not clear from the data I've seen how many of the tests in Switzerland are community tests as opposed to tests of people who have symptoms. That would be interesting to know.
Exactly, the very important number is the prevalence of Covid in the tested group. If people with symptoms are tested, then the prevalence would be higher than in case of testing any person randomly.

I don't think the tests in Switzerland are conducted only on people with symptoms though. To name just a few groups which are routinely tested without symptoms -- doctors, nurses, old age home workers, travelers, family members of positive cases, contacts of positive cases. There are a lot of people without symptoms being tested. The Covid prevalence in these groups is very low. We might have a big number of false positives!

And if we imagine for a moment that all Covid is gone from Switzerland. In this case we still will have thousands of positive tests if we keep testing at the same rate. Suppose that the test sensitivity at 95%. This means that for 50K of tests we will get around 5% (2500 cases) positives, all of them false. The point is -- we will never go to zero cases by applying the current testing.

P.S. How nice this page is number 1'000, the post is number 20'000, and the thread is one year old!

Last edited by leonie; 25.01.2021 at 20:15.
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