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asperity
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There were 15,526 truck drivers in Kent tested before they were allowed to cross the Channel, with 36 positive results. This comes out as a 0.23% positive result from what was a truly random sample of people who had arrived in Kent from all around the country.  Just saying............................................🙄🤔

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Or looked at in a different way Asp, 36 who just days earlier tested clear had now become infected. The sample can’t be said to be random because most had been tested and shown to be clear before entering the UK so this only shows what’s changed in a period of a few days.

 

Bill 😊

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All these tests prove is that you are negative at the point the test was taken, so is useful for screening entry to high risk areas.   It doesn't stop subsequent contamination and spread, so would need to be repeated every time one is screened for entry.   The trace element of a system is designed locate spread from a source, and is more useful in tracing outbreak sources,  when the virus is more or less under control.  😷

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I think we’re a million miles past the point where we could say it’s under control so test and trace as such is a total waste of time especially where people are still so mobile. The testing bit maybe help to catch and stop some spreading, but the tracing regime never really worked from day one.

 

Bill 😊

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5 hours ago, Observer II said:

According to the news, there's  a run on hospital beds for covid cases at the moment - just saying ...........      😷   :rolleyes:

Hospitals are always under pressure from respiratory conditions at this time of year - just saying...................🙄

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3 hours ago, Davy51 said:

I suppose in the case of wagon drivers it is possible that their point of close contact with other people & therefore susceptibility to infection from others is somewhat limited considering they are generally in a solitary bubble for days at a time.

Very true - perhaps truck drivers don't interact with other truck drivers at all. Or perhaps this shows that the virus isn't as contagious as is thought if they do interact when stuck in a lorry park for a few days with hundreds of fellow truck drivers. Something to ponder.

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Quote

Perhaps this shows that the virus isn't as contagious as is thought

Take 15526 drivers, test them to show they’re virus free then get them to mix in a car park for five days and how many should catch the virus? The answer of course is none, but 38 were infected at some point during their visit, despite spending most of their time relatively isolated in their cabs.

Now if instead of 15526 tested Johnny foreigners, we took that number of untested Brits and did the same, then I suspect the figures would be quite different. Therefore, no comparisons or conclusions can be drawn as these numbers are neither statistically random nor typical of what we have here now.

It’s all too easy to read into things like this and end up with a completely different result depending on one’s point of view in the first place.

 

Bill 😊

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There can be quite a big difference between foreign drivers heading home as opposed to domestic UK drivers. Johnny foreigner will be using the same vehicle all the time whereas UK drivers ,being on home turf, could well be using a variety of multi manned vehicles. Do we know which drivers have tested positive, for instance ?

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You are, of course, correct Bill except for all the assumptions you are making (that they were all foreigners, that they spent most of their time relatively isolated in their cabs). I'm not drawing any conclusions, my original post was just a report on what had been found in this case, leaving you all to make of it what you will 😉

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49 minutes ago, Observer II said:

The UK has recorded a record of  over 41,000 new cases of covid yesterday - just saying. 😷

Which, as a percentage of tests done, is slightly lower than the average. Cases are the number of positive tests and not the number of people presenting as being ill with Covid which, given that there are a lot of false positives, means the number isn't as scary as you would like to make out.

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Oh come on Asp, you should know by now that even my wildest assumptions are always correct. 😊

As for today’s figures, yes. they’re not particularly high, but when have Monday’s numbers ever been correct? I suppose we’ll just have to wait another week or so get the true picture of what happened over Christmas and whether the anticipated spike occurred.

 

Bill 😊

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3 hours ago, asperity said:

Which, as a percentage of tests done, is slightly lower than the average. Cases are the number of positive tests and not the number of people presenting as being ill with Covid which, given that there are a lot of false positives, means the number isn't as scary as you would like to make out.

What actual evidence do you use to claim that there a lot of false positives please? In Warrington during the 7 days leading to 23/12 there were 9.8% of people tested had a positive test. That had gone up from 6% on the 8/12. This shows that the numbers are going up because of higher prevalence and not just more testing.  It just isn't a given that there are a lot of false positives in PCR tests for people who are exhibiting symptoms, that is used at the right time. 

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I think we will have to wait a lot longer than a week or so (a year or so?) to get a true picture of what has happened.

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9 minutes ago, Confused52 said:

What actual evidence do you use to claim that there a lot of false positives please? In Warrington during the 7 days leading to 23/12 there were 9.8% of people tested had a positive test. That had gone up from 6% on the 8/12. This shows that the numbers are going up because of higher prevalence and not just more testing.  It just isn't a given that there are a lot of false positives in PCR tests for people who are exhibiting symptoms, that is used at the right time. 

The Lancet reported that false positives could be between 0.8% and 4% of PCR tests. Evidence of anything is pretty hard to come across to be honest.

Interesting caveats you attach to your statement though.

I'm not trying to claim anything, just trying to make sense of all the information and misinformation being bandied about and think that a lot of people are under the impression that they are going to die if they stick their noses outside the front door. By the same token there are a lot of people who think they are fireproof!

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25 minutes ago, asperity said:

The Lancet reported that false positives could be between 0.8% and 4% of PCR tests. Evidence of anything is pretty hard to come across to be honest.

Interesting caveats you attach to your statement though.

I'm not trying to claim anything, just trying to make sense of all the information and misinformation being bandied about and think that a lot of people are under the impression that they are going to die if they stick their noses outside the front door. By the same token there are a lot of people who think they are fireproof!

That range comes from a SAGE paper (Carl Mayers & Kate Baker, 3rd June 2020) which said:

"An attempt has been made to estimate the likely false-positive rate of national COVID-19 testing programmes by examining data from published external quality assessments (EQAs) for RT-PCR assays for other RNA viruses carried out between 2004-2019 [7]. Results of 43 EQAs were examined, giving a median false positive rate of 2.3% (interquartile range 0.8-4.0%).:"

The answer from PHE is to use the low positive cases detected by the ONS survey during the summer when they were doing tens of thousands of tests per week even when the incidence was low.  ONS said on 14th May:

"Uncertainty in the test (false-positives, false-negatives and timing of the infection)

These results are directly from the test, and no test is perfect. There will be false-positives and false-negatives from the test, and false-negatives could also come from the fact that participants in this study are self-swabbing. We also do not know if all individuals testing positive are still infectious; it is possible some may have had COVID-19 in the past but still test positive. We do not know the exact false-positive or false-negative rate of the current swab test for the virus. However, based on the very low number of positives in the results so far, we know the false-positive rate is very low (as even if every single positive result was false, this rate could only be 0.30%). We do not have information on the false-negative rate."

There is a difference between the operational rate and the rate for characterising the test. The ONS rate is operational and clearly represents an over estimate.

Note their caveats too. When used at the right time (again) the false positive rate is very low. Many claims suggest that the test triggers on proteins not from covid but they test for three sequences not just one. The recent new variant did not trigger the test for the S protein and it was that they used to estimate the prevalence but 2 out of three were still positive. They have now tweaked the test.

Does that help I wonder?

 

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9 hours ago, Confused52 said:

That range comes from a SAGE paper (Carl Mayers & Kate Baker, 3rd June 2020) which said:

"An attempt has been made to estimate the likely false-positive rate of national COVID-19 testing programmes by examining data from published external quality assessments (EQAs) for RT-PCR assays for other RNA viruses carried out between 2004-2019 [7]. Results of 43 EQAs were examined, giving a median false positive rate of 2.3% (interquartile range 0.8-4.0%).:"

The answer from PHE is to use the low positive cases detected by the ONS survey during the summer when they were doing tens of thousands of tests per week even when the incidence was low.  ONS said on 14th May:

"Uncertainty in the test (false-positives, false-negatives and timing of the infection)

These results are directly from the test, and no test is perfect. There will be false-positives and false-negatives from the test, and false-negatives could also come from the fact that participants in this study are self-swabbing. We also do not know if all individuals testing positive are still infectious; it is possible some may have had COVID-19 in the past but still test positive. We do not know the exact false-positive or false-negative rate of the current swab test for the virus. However, based on the very low number of positives in the results so far, we know the false-positive rate is very low (as even if every single positive result was false, this rate could only be 0.30%). We do not have information on the false-negative rate."

There is a difference between the operational rate and the rate for characterising the test. The ONS rate is operational and clearly represents an over estimate.

Note their caveats too. When used at the right time (again) the false positive rate is very low. Many claims suggest that the test triggers on proteins not from covid but they test for three sequences not just one. The recent new variant did not trigger the test for the S protein and it was that they used to estimate the prevalence but 2 out of three were still positive. They have now tweaked the test.

Does that help I wonder?

 

Does that help I wonder?

Not really. They seem pretty sure that they are unsure, but I'm no expert at translating gobblydegook 🤔

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Why do you think we’d have to wait a year Asp when we know how short the incubation time is? I believe there was a significant spike in the numbers in the US about a week after Thanksgiving so I suppose much the same will happen here.

I doubt many of us fully understand the numbers and the science behind all this. I have a good understanding of sampling and probability theory which helps but genetics is all black magic and gobbledygook to me. So, we don’t have any option but to trust those who do understand these things and accept the fact that nobody in their right mind would want to propagate false information when for society, there’s nothing to gain.

 

Bill 😊

 

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I'm thinking more of the time it will take for the true story about the pandemics given the huge number of people who will need time to cover their backsides 😉.

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2 hours ago, asperity said:

Does that help I wonder?

Not really. They seem pretty sure that they are unsure, but I'm no expert at translating gobblydegook 🤔

PHE were effectively responding to the SAGE action to remove uncertainty. They realised, correctly, that the experts on such statistical works are the ONS. The ONS survey is of people at random who are not known to have an infection. That is an important point because their estimate is based on a worst case interpretation of their results. The rate of 0.30% false positives assumes every positive case was false and therefore gives an upper bound and worst case value for tests using PCR. They seem to have used this convoluted method to avoid giving out multiple different values. I heard of this result on More or Less on Radio4 from Professor David Spiegelhalter who was asked what the false positive rate was.

The unsure bits you mention don't seem very uncertain to me the just seem scientifically cautious. For example, they could have included that they didn't check that people swapped samples with a known infected person just to be malicious. I suggest that they do know pretty well what the accuracy of the test is on random samples of mostly non infected people. When people have symptoms and have asked for a test they are going to show a lower error rate but the 0.30% error rate will still apply to those who are tested as contacts having not shown symptoms. That hopefully explains the point I made in the earlier post. The test also has false negatives and they are much harder to pin down as you can see.

I concentrated on the issue of false positives because there as a set of people claiming the false positive rate is high to make a claim that the epidemic is somehow overstated. 

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