Chat about Novel Coronavirus - 2019-nCoV - COVID-19

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Greenbank in reply to @Lebowski

It has a 100% sensitivity and 97.5% specificity.

That's what they claim, it later says:-

In the laboratory’s study, the test had a sensitivity of 98.5% which means that if 1,000 people who had previously been infected with coronavirus virus took the test, 15 of them would be told that they hadn’t had coronavirus when they had (a false negative result). It had a specificity of 99.5% which means that if 1,000 people who hadn’t had the virus took the test, 5 of them would be told they had been infected when they hadn’t (a false positive result).

So if 5% of the population have had it then using 98.5% and 99.5% figures we get:-
-ve result would be 99.973% accurate
+ve result would be 91.284% accurate

If 1% of the population have had it then:-
-ve would be 99.995% accurate
+ve would be 66.779% accurate

If 10% of the population have had it then:-
-ve would be 99.944% accurate
+ve would be 95.673% accurate

(Caveat my fat fingers mistyping something into a spreadsheet.)

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in reply to @Greenbank

So if 5% of the population have had it then using 98.5% and 99.5% figures we get:-

-ve result would be 99.973% accurate
+ve result would be 91.284% accurate

If 1% of the population have had it then:-
-ve would be 99.995% accurate
+ve would be 66.779% accurate

If 10% of the population have had it then:-
-ve would be 99.944% accurate
+ve would be 95.673% accurate

What are you doing to get a shift in sensitivity/specificity based on an outside factor?

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frankenbike in reply to @

Bayesian statistics as described on the previous page. Interesting stuff.
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Greenbank in reply to @

The sensitivity and specificity aren't changing. The derived accuracy of a result changes depending on how prevalent the condition is amongst the tested population as the relative

The less prevalent the condition is in the population the more false positives you'll get.

The more prevalent the condition is in the population the more false negatives you'll get.

Both of these factors affect the eventual accuracy. See: https://www.lfgss.com/comments/15296147/

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