@enhydra lutris @enhydra lutris
beyond the large comment I posted below.

A diagnostic test has a "sensitivity" and a "specificity". These refer to how it behaves with respect to actual samples.

The RT-PCR tests appear to have a sensitivity nearing 100% (and yes, it depends on the much-discussed-by-folks-who-don't-really-understand PCR cycles). If I test a positive sample, there's a 99.lots % chance I'll detect the virus.

The RT-PCR tests appear to have a specificity of about 99.5%. This means that if I test a negative sample, there's a 99.5% chance the test will report that the sample is negative.

Where things get tricky is when I'm testing a population in which a very large fraction of samples are truly negative. Hell, let's just say the test has 99.5% sensitivity AND 99.5% specificity. If I test 10,000 people, and only 1% of the samples I'm testing are truly positive, then I'll get 100 "true positives", but 0.5% of my 9,900 negative samples will also test positive -- that's about 50. So I'll have 150 positives, but [EDIT for typo] 50 of those -- a disturbing 33% -- will be "false positives".

On the other hand, if 5% of the samples I'm testing are actually positive, then I'll get 500 true positives and about 50 "false positive" -- about 9%. And if 10% of the samples I'm testing are actually positive, then I'll get 1000 "true positives" and 45 "false positives" -- 4.5ish%.

#1

My cursory search turned up the following ranges 0.4% - 0.7%, 0.5% - 0.8%, and 0.4% to 0.9%. It seems that the 2 Brits with a blog were off by a factor of roughly 100. After all, if you don't focus, 0.5% looks a lot like 50%

be well and have a good one

@UntimelyRippd @UntimelyRippd If you have not seen this paper, you might like to check it out:

https://cormandrostenreview.com/report/

In mid-January of this year, a paper outlining how to do PCR testing for Covid19 was submitted to the journal Eurosurvelliance by lead researcher Dr. Christian Drosten and associated authors. That paper was then used by the WHO as the basic recommendation for subsequent PCR tests. Recently, a group of 22 scientists did a peer review of the original Drosten paper, and found serious errors, such that they felt there was an overwhelming case the paper should be withdrawn. In their review, they did address the fact that the PCR test, as designed, could not distinguish between live and dead virus fragments.

The Abstract of the paper:

ABSTRACT

In the publication entitled “Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR” (Eurosurveillance 25(8) 2020) the authors present a diagnostic workflow and RT-qPCR protocol for detection and diagnostics of 2019-nCoV (now known as SARS-CoV-2), which they claim to be validated, as well as being a robust diagnostic methodology for use in public-health laboratory settings.

In light of all the consequences resulting from this very publication for societies worldwide, a group of independent researchers performed a point-by-point review of the aforesaid publication in which 1) all components of the presented test design were cross checked, 2) the RT-qPCR protocol-recommendations were assessed w.r.t. good laboratory practice, and 3) parameters examined against relevant scientific literature covering the field.

The published RT-qPCR protocol for detection and diagnostics of 2019-nCoV and the manuscript suffer from numerous technical and scientific errors, including insufficient primer design, a problematic and insufficient RT-qPCR protocol, and the absence of an accurate test validation. Neither the presented test nor the manuscript itself fulfils the requirements for an acceptable scientific publication. Further, serious conflicts of interest of the authors are not mentioned. Finally, the very short timescale between submission and acceptance of the publication (24 hours) signifies that a systematic peer review process was either not performed here, or of problematic poor quality. We provide compelling evidence of several scientific inadequacies, errors and flaws.

Considering the scientific and methodological blemishes presented here, we are confident that the editorial board of Eurosurveillance has no other choice but to retract the publication.

#1
big fat liars who don't know what they're talking about, even when they should -- such as the well-credentialed UK epidemiologist who stated categorically that we were "through" the pandemic -- 6 months and 25,000 dead Britons ago. BTW, Britons are currently dying at close rates to Americans -- about 3000/week, or 0.23% annually, vs 17,000/week (0.27% annually), which I do understand is considered by some people to be quite small and nothing to be fussed about, but YMMV. In any case, they have certainly not seen the last of the pandemic, and of course, that person's suggested ceiling on infection fatality rate -- 0.1% -- has been revealed as the insanity it always was, since the actual mortality rate -- not IFR, but overall mortality rate -- has now exceeded 0.1% in several places, including the UK (and probably the US, where 10s of thousands of Covid deaths have not been counted as such). Regionally, it has exceeded 0.1% in 17 American states, and in some it has or is soon to exceed 0.2% (e.g. New Jersey already there, New York State and the Dakotas will both cross that threshold in the next 4 weeks, possibly 3, and Connecticut, Rhode Island and Massachusetts are all seeing rates that will get them there before Valentine's Day.)

Yes, in regions where infection rates are low (under 1 or 2%), and people are being tested randomly (as opposed to in response to symptoms), the rate of positive results reported that come from actually negative samples can approach 50%. (I mean, theoretically, it can be 100%, because somewhere between 1.0% and 0.1% of actually negative samples will test positive ... so if nobody is infected, and you test 1000 people, you'll get a handful who test positive, and 100% of those positives are false.)

However: When 5% or 10% or (as in the Dakotas, where the population has decided that if God wants Grandma so much that he'll take her unless people wear masks, then God will just get what he wants, because he's God, you know, and masks are satanic inventions of sociamalists, or maybe socialist inventions of satanists, or something ...) 20%+ of the population being tested are true positives, those true positives start to seriously outnumber the false positives, and the false positive rate collapses to single-digits.

And to my knowledge (which I admit is not all-encompassing), there is no empirical support for the notion that the RT-PCR tests detect fragments of viral RNA left behind weeks after the infection has been suppressed by your body. It just seems to be something that some people are saying. It would be easy to design an experiment for finding out, but I don't know of one that's been reported. It seems unlikely, because RNA is quite short-lived inside a living cell -- half-life of less than 10 hours.