Test Yourself Frequently for Covid - 19. Stay Safe

[TrueTomHarley]

IMG_6342.mov

[admin]

I’m gonna need a lot more wine. 

[JW Insider]

Pretty funny. Except that it tends to spread a false narrative about false positives. It's based on what Dom Raab said. (In the video, she mentions him right from the start.) It's explained pretty well here:

Dominic Raab did not say Covid-19 tests have a 93% false positive rate

https://fullfact.org/online/dominic-raab-93-percent/

But the article admits that he really did say nearly the equivalent of that, but that he was wrong. He was confusing false positives with false negatives. (And what he said feeds into a false but popular belief that the PCR tests don't work.) Here's an excerpt:

The false positive rate means the percentage of tests that wrongly tell people who do not have the virus that they are infected. Tests can also produce false negatives, where people who do have the virus are told they don’t.

It appears Mr Raab was referencing a PHE report, which stated that the success rate of identifying Covid cases when only testing travellers on arrival at airports is 7%. By testing on arrival and then testing again five days into self isolation, the success rate goes up to 88%. 

Mr Raab appears to have mis-spoken, as the PHE report doesn’t talk about false positives at all. 

It’s actually referring to false negative results: incoming travellers who are infected, but who might not be identified by a single test at an airport. This can be due to factors such as the virus’s incubation period, when an infected person might still test negative due to the low levels of virus in their body.

In addition, the PHE study is not based on real-life data. It is simply a modelling study intended to explore how different isolation and testing regimes might improve the chances of identifying infected travellers. Like all models, it simplifies things and makes some assumptions that may not reflect reality.

It’s not possible to establish a definitive false positive rate for Covid-19 testing, as this can vary according to circumstance, but as we have written elsewhere there is good evidence that false positives are extremely rare with the RT-PCR tests that are used for most testing in the UK.