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  #16921  
Old 21.11.2020, 21:15
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Re: Coronavirus

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If the false positive rate is 2% & you only have a positive rate of 2%, it's possible that there are zero infections.
Therefore with 3% of positives 1/3 will likely be positive & 2/3 false positives. However if 10% of tests are positive then 80% will likely be positive & 20% false positive.
e.g.
100 people are tested
2% test positive = 2 people
2% are false positives = 0.04 people.
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  #16922  
Old 21.11.2020, 21:18
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Re: Coronavirus

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e.g.
100 people are tested
2% test positive = 2 people
2% are false positives = 0.04 people.

Your working out would require 100% of positive test results to be false positives.
Unfortunately thats not correct, I used to think it was.

No, if a high no of tests are positive, then they will be fairly accurate, when a low no of tests are positive it's inaccurate.

From FDA https://www.fda.gov/medical-devices/...cal-laboratory

Remember that positive predictive value (PPV) varies with disease prevalence when interpreting results from diagnostic tests. PPV is the percent of positive test results that are true positives. As disease prevalence decreases, the percent of test results that are false positives increase.
For example, a test with 98% specificity would have a PPV of just over 80% in a population with 10% prevalence, meaning 20 out of 100 positive results would be false positives.
The same test would only have a PPV of approximately 30% in a population with 1% prevalence, meaning 70 out of 100 positive results would be false positives. This means that, in a population with 1% prevalence, only 30% of individuals with positive test results actually have the disease.
At 0.1% prevalence, the PPV would only be 4%, meaning that 96 out of 100 positive results would be false positives.
Health care providers should take the local prevalence into consideration when interpreting diagnostic test results.
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  #16923  
Old 21.11.2020, 21:33
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Re: Coronavirus

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I'm sorry but this doesn't make any sense.
If you read my link from the FDA it might https://www.fda.gov/medical-devices/...cal-laboratory

"At 0.1% prevalence, the PPV would only be 4%, meaning that 96 out of 100 positive results would be false positives."
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  #16924  
Old 21.11.2020, 21:36
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Re: Coronavirus

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If the false positive rate is 2% & you only have a positive rate of 2%, it's possible that there are zero infections.
Therefore with 3% of positives 1/3 will likely be positive & 2/3 false positives. However if 10% of tests are positive then 80% will likely be positive & 20% false positive.
Ah back on that idiotic claim are you?

It's actually very easy to demonstrate. In the summer Switzerland had weeks with a corona positive rate below 0.7%. Even if all those positives were false, the false positive rate cannot be above 0.7%.

In reality of course most of them were correct - the true rate of false positives is something below 0.1%.

Edit - 16th June there were 10,045 tests and a massive 21 positive (BAG dashboard figures). That's actually only 0.2% positive on a large sample size. There's your maximum positive rate.
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  #16925  
Old 21.11.2020, 21:36
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Re: Coronavirus

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Unfortunately thats not correct, I used to think it was.

No, if a high no of tests are positive, then they will be fairly accurate, when a low no of tests are positive it's inaccurate.

From FDA https://www.fda.gov/medical-devices/...cal-laboratory

Remember that positive predictive value (PPV) varies with disease prevalence when interpreting results from diagnostic tests. PPV is the percent of positive test results that are true positives. As disease prevalence decreases, the percent of test results that are false positives increase.
For example, a test with 98% specificity would have a PPV of just over 80% in a population with 10% prevalence, meaning 20 out of 100 positive results would be false positives.
The same test would only have a PPV of approximately 30% in a population with 1% prevalence, meaning 70 out of 100 positive results would be false positives. This means that, in a population with 1% prevalence, only 30% of individuals with positive test results actually have the disease.
At 0.1% prevalence, the PPV would only be 4%, meaning that 96 out of 100 positive results would be false positives.
Health care providers should take the local prevalence into consideration when interpreting diagnostic test results.

The link refers to antigen tests - this is a different type of test. I specificslly talked about PCR which was the claim on this crazy "take your mask off" poster.
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  #16926  
Old 21.11.2020, 21:39
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Re: Coronavirus

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Ah back on that idiotic claim are you?

It's actually very easy to demonstrate. In the summer Switzerland had weeks with a corona positive rate below 0.7%. Even if all those positives were false, the false positive rate cannot be above 0.7%.

In reality of course most of them were correct - the true rate of false positives is something below 0.1%.
If you read what the FDA wrote, I have linked it twice, the false positive rate could have been close to 100% with a positive rate of 0.7%
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Old 21.11.2020, 21:41
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Re: Coronavirus

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The link refers to antigen tests - this is a different type of test. I specificslly talked about PCR which was the claim on this crazy "take your mask off" poster.
Indeed, however it explains the maths behind false positives which the majority of the population have not understood.
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Old 21.11.2020, 21:45
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Re: Coronavirus

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If you read what the FDA wrote, I have linked it twice, the false positive rate could have been close to 100% with a positive rate of 0.7%
0.7% is already tiny. Except as I added in the edit the actual figures confirm it is below 0.2%. Of all tests. I severely doubt it is even as high as 0.05%.

Even 0.2% is negligable in terms of total coronavirus numbers. The test is extremely accurate by any reasonable standards.
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  #16929  
Old 21.11.2020, 21:49
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Re: Coronavirus

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A positive PCR test does not mean you are infected, approx a 2% false positive rate, so when positives are around 3% then there is about a 33% chance that you have Covid. It's quite possible that the majority of people without symptoms are false positives.
You really do not understand statistics, do you.
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  #16930  
Old 21.11.2020, 22:07
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Re: Coronavirus

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No, unfortunately not, the test is not very accurate, it's caused huge hysteria due to the no of 'cases'. The UK's NHS will only test people with symptoms for this reason.
People with symptoms of Covid also test negative, I suspect quite often. Virus is in your upper respiratory tract only at the beginning of the infection. Beginning of Covid19 infection is very often mild thus people don't even bother to show up at hospitals or testing sites.
Belgium stopped using positive negative language to describe test results and now calls test results DETECTED/NOT DETECTED.

P.S. When I ended up in a hospital with Covid symptoms I tested negative in ER. I spent 2 days in a hospital and was sent home and told I don't have Covid. I did not believe their test results due to my symptoms being so unusual, matching most Covid symptoms and also novel.
I've tested positive for antibodies to Covid 3 months later.
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Old 21.11.2020, 22:09
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Re: Coronavirus

Just re-watching a very interesting movie, given these troubling times. "V for Vendetta" made in 2005 and starring Natalie Portman. I watched this years ago and the parallels are pretty staggering re: today.

In short, the film takes place in London 2020, and society is under lockdown because of a virus. Unbeknowst to the population, the virus was manufactured and leaked via a government facility (hmmm) ...

Anyway, it is a thought provoking, prescient movie and entertaining.
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  #16932  
Old 21.11.2020, 22:16
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Re: Coronavirus

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Just re-watching a very interesting movie, given these troubling times. "V for Vendetta" made in 2005 and starring Natalie Portman. I watched this years ago and the parallels are pretty staggering re: today.

In short, the film takes place in London 2020, and society is under lockdown because of a virus. Unbeknowst to the population, the virus was manufactured and leaked via a government facility (hmmm) ...

Anyway, it is a thought provoking, prescient movie and entertaining.
ohh, those timetravellers
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  #16933  
Old 21.11.2020, 22:16
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Re: Coronavirus

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0.7% is already tiny. Except as I added in the edit the actual figures confirm it is below 0.2%. Of all tests. I severely doubt it is even as high as 0.05%.

Even 0.2% is negligable in terms of total coronavirus numbers. The test is extremely accurate by any reasonable standards.
This explains it well, it's nothing like as reliable as you are claiming.

https://www.icd10monitor.com/false-p...s-for-covid-19
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  #16934  
Old 21.11.2020, 22:27
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Re: Coronavirus

You have to congratulate Sweden for not panicking and indirectly killing more people than the virus itself, their excess mortality for 2020 so far seems to be 2000 more than their worst year in the last 5 years out of 90k deaths per year happening in the country

Proof that without lockdown and without useless masks for general population the virus can be controlled and managed!

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  #16935  
Old 21.11.2020, 23:08
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Re: Coronavirus

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This explains it well, it's nothing like as reliable as you are claiming.

https://www.icd10monitor.com/false-p...s-for-covid-19
Interesting indeed! Hadn't thought that through.

At current positivity rates in Switzerland though, this means that test results are showing too few actual positives.
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  #16936  
Old 21.11.2020, 23:11
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Re: Coronavirus

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Interesting indeed! Hadn't thought that through.

At current positivity rates in Switzerland though, this means that test results are showing too few actual positives.
Correct
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  #16937  
Old 21.11.2020, 23:16
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Re: Coronavirus

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Unfortunately thats not correct, I used to think it was.

No, if a high no of tests are positive, then they will be fairly accurate, when a low no of tests are positive it's inaccurate.

From FDA https://www.fda.gov/medical-devices/...cal-laboratory

Remember that positive predictive value (PPV) varies with disease prevalence when interpreting results from diagnostic tests. PPV is the percent of positive test results that are true positives. As disease prevalence decreases, the percent of test results that are false positives increase.
For example, a test with 98% specificity would have a PPV of just over 80% in a population with 10% prevalence, meaning 20 out of 100 positive results would be false positives.
The same test would only have a PPV of approximately 30% in a population with 1% prevalence, meaning 70 out of 100 positive results would be false positives. This means that, in a population with 1% prevalence, only 30% of individuals with positive test results actually have the disease.
At 0.1% prevalence, the PPV would only be 4%, meaning that 96 out of 100 positive results would be false positives.
Health care providers should take the local prevalence into consideration when interpreting diagnostic test results.
To look at the math behind the tests, here is the FDA article “EUA Authorized Serology Test Performance” about the test performance characteristics and limitations:
https://www.fda.gov/medical-devices/...st-performance

and the FDA test calculator
https://www.fda.gov/media/137612/download

and the CDC instructions and examples on the FDA test calculator
https://www.cdc.gov/coronavirus/2019...calculator.pdf
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  #16938  
Old 22.11.2020, 00:02
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Re: Coronavirus

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Facing another retirement home lockdown, 90-year-old chooses medically assisted death
https://www.ctvnews.ca/mobile/health...eath-1.5197140
This woman's choice makes complete sense to me. The only part I'd take issue with are the criteria by which someone qualifies for MAID (medically assisted death). According to the article:
In Canada, you do not need to have a fatal or terminal condition to apply for MAID, but you must have a serious condition, be in an advanced stage of irreversible decline, be experiencing mental of physical suffering that cannot be relieved and be at the point where “your natural death has become reasonably foreseeable.”

The woman had previously applied for assisted death, but was first turned down because she did not fulfil all the criteria. It seems terribly presumptious to tell a compus mentis 90-year-old who has seen life, and taken an assessment of all of her circumstances and her own condition, that she's not allowed to die in dignity, the way she wants to.

By the time she'd decided that lockdown restricted her life too much, she'd developed further ailments which tipped the balance, so that her second application was successful. From the article:
“I do want to underscore the fact that she wanted medical assistance in dying at some point,” her daughter stressed. “And she had told her family doctor that, but the application was hastened by the impact of the lockdown measures.”
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  #16939  
Old 22.11.2020, 00:11
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Re: Coronavirus

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The link refers to antigen tests - this is a different type of test. I specificslly talked about PCR which was the claim on this crazy "take your mask off" poster.
I think you are right, PCR tests are based on gene technology and extremely specific. Specificity of most PCR tests is close to 100%, and this would give few false positive results even when the prevalence is low. When looking at other tests for understanding the numbers, it is good to remember that these are different types of tests from the PCR test.

On the other hand, even though PCR tests are 100% specific because of the technology used, in real life nothing is 100%, and probably nobody knows what the real number of false positive PCR tests is due to human errors.

Last edited by leonie; 22.11.2020 at 00:36.
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  #16940  
Old 22.11.2020, 09:03
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Re: Coronavirus

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While not denying peoples fundamental human rights to choose not to be vaccinated and immunised against Covid19 if they don't want to.
I disagree. I don’t see this choice being a fundamentally human right. I see it as a fundamental human responsibility. Unless you want to live in a cave somewhere and eschew all human contact. And even then as someone eventually will need to deal with your remains.

As well covering the cost of vaccinations should be born by the nation.
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