5 ms·
If the false positive of the PCR test really is 2.3%, how are so many places able to have positivity rates consistently less than that, more like .1%[1]? And ho
by tuna-piano 6y ago
If the false positive of the PCR test really is 2.3%, how are so many places able to have positivity rates consistently less than that, more like .1%[1]? And how can test pooling in huge numbers (like was done in Wuhan) work?
A false positive rate that high doesn't pass the sniff test.
[1]https://ourworldindata.org/coronavirus-testing https://ourworldindata.org/coronavirus-testing
[2]https://www.nytimes.com/2020/05/26/world/asia/coronavirus-wuhan-tests.html https://www.nytimes.com/2020/05/26/world/asia/coronavirus-wu...
- wjn0 6y agoI'm not sure if this is it, but assuming the correctness of the test is independent of the sample quality, a sample could be split and tested multiple times to obtain a result with a much better FPR.
- mehrdadn 6y agoAnecdotally I've heard this isn't the case, but I don't have links.
- cameldrv 6y agoTo my knowledge, the most common failure mode is that the concentration of viral RNA in the sample is below the limit of detection. This could be because the swab wasn't done correctly, the patient wasn't shedding very much virus, the sample was mishandled (heat can break down the sample), or the sample wasn't adequately mixed.
- goalieca 6y agoThere is a relatively massive false negative rate.
- repsilat 6y agoRegardless of false negative rate, measured positives are always at least as frequent as false positives.
- nl 6y agoSome specific tests seem too sensitive. Different tests are used in different jurisdictions and at different times.