Yes, when I want to know what the WHO says then I read what the WHO says. I know that can be confusing when there are nutty conspiracy that can be promoted.
WHO: A positive PCR test does not in itself constitute infection
- Thread starter IRIS
- Start date
Did you not read the OP? The WHO is linked even if the blogger wasn't able to understand what it says.
Fair. Still nice knowing I can equally make that informed choice with that additional piece of pertinent information.
I insist, continue to share your wacky conspiracy theories.
Not only that, the highlighted line This means that the probability that a person who has a positive result (SARS-CoV-2 detected) is truly infected with SARS-CoV-2 decreases as prevalence decreases, irrespective of the claimed specificity is just a basic truth about any detection test. Unless you have a test that never gives a false positive ever (100% never no matter who is administering it or how it is handled) then the above statement is true.
If the test only gives false positives 1 in a million times, then if you test 10 million people you will get 10 false positives.
If only 10 people in that 10 million have the disease in the ten million have the disease, then youget 20 positives - a 50% false positive rate.
If 1000 people in the 10 million have the disease then there will be 1010 positive results - a <1% false positive rate.
It's the most uncontroversial thing in the world.
It is. Digging into the FAQ they have this.
Sensitivity is how often if someone is positive, they show up as positive on the test. In other words a 70-90% sensitivity means that if I am positive, there is a 70-90% chance I will show up as positive in the test. (What that probably means is that when someone has low levels of virus in the system, they might get missed.)
Specificty is how often if someone is negative, they show up as negative on the test. In other words, >99% specificity means that if I am negative, I will show up as a false positive <1% of the time.
They show some other numbers because obviously you have to test these numbers all kinds of ways.
But this kind of result for false positives
is excellent for a diagnostic test.
Yeah dont you wish we only had 1 in a million false positives lol
Even at top tier labs false positives are way higher than that
Even based on Public Health Ontario own numbers (at a very highly rated / respected lab)
They also go on to discuss what they call subclinical cases (other sources refer to these as false positives; they are not BUT they can not spread)
But it may be a subclinical case, meaning that your viral load is so low that you are not infectious and cannot spread the virus to other people, including those in your immediate household — which is a good thing!
The 1 in a million false positives was to make the math easy to explain and show how the statement about prevalence being important in terms of overall numbers of false positives.
According to that paper you linked, there are roughly 20 false positives per 228,000 tested. Closer to 1 false positive for every 10,000 tests.
If that held and you tested the entire population of Ontario (~14.5 million) you would get 1,272 false positives.
Yes, and this is one of the reasons I argue that PCR is good for diagnosing, but not useful for population screening in terms of getting people back to work. Faster, cheaper, lower-sensitivity tests would be better, even if they had a much higher false positive rate. For a screening test to open the economy you would want tests that were excellent at avoiding false negatives. Of course, the people who think COVID-19 is fake would complain about the false positives in that scenario, which I am sure is part of the political pressure preventing shifting to those tests.
Obviously, the ideal would be a fast, cheap test that had excellent sensitivity AND specificity but it is really rare for a test to excel at both.
Please share with me if you believe the world is flat and if you keep driving in one direction for too long you will fall off into oblivion or maybe something far more sinister?
It's funny that you quote the exact same document that was previously quoted to try and say the exact opposite.
5. Q. What is the incidence of false positive COVID-19 tests? What is the cause of this and what is done to minimize this from occurring? A. Based on PHO Laboratory data, we are aware that the incidence of false positive tests that are later corrected is extremely low. The exact incidence for the province is not known, as individual reports that are corrected do not require notification. As of May 23, 2020, PHO Laboratory has detected false positive SARS-CoV-2 results on approximately 20 occasions among over 228,000 specimens tested to date for COVID-19, with ~11,000 specimens testing positive. This represents a false positivity rate of less than 0.01% (specificity of >99.99%), which is well beyond performance targets for a laboratory test, even acknowledging there may be some false positive tests that are not detected. In general, the positive predictive value of COVID-19 PCR assays is excellent, and approaches 100%. At PHO Laboratory, we know this as we are able to generate viral sequence from samples that are positive provided the viral copy number is not near the lower limit of detection of the assay.
p.s. According to the government, Ontario has completed 9.9 million tests as of yesterday and 276,718 positives. At the rate quoted by TJ's source, that would mean a total of 842 false positives.
But no, let's go with TJ's fairy tale that we've had millions of false positives out of the less than 300,000 cases.
But no, let's go with TJ's fairy tale that we've had millions of false positives out of the less than 300,000 cases.
I cannot help but to think that her political and personal views -- which she shares on these boards quite freely -- have cost her a LOT of business.
