Current Page: 1 of 2
Testing, testing
Posted by: Tom Paine (IP Logged)
Date: 08 July, 2020 16:29

After the first round of testing at all 12 Prem clubs (804) tests, 6 players and 4 staff have tested positive to Coronavirus. They have not been named, but this is after non-contact training Hope all recover without lasting effects. Source: BBC Sport

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 08 July, 2020 22:59

I wonder if anyone has read this article?

gov.uk
there is a very serious issue here (not just for sports)
When prevalence is so low then the false positive rate when testing symptom-less subjects is a big problem.
It is known as "The Base Rate Fallacy" for those who want to explore it further!!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.

Re: Testing, testing
Posted by: Tiggs (IP Logged)
Date: 08 July, 2020 23:14

10 test positive, with one at Saints and more than one at Sarries, an unknown number at Quin's, and others not mentioned.
That is out of just 804 tests, and before contact training.
Doesn't look good for a return to playing soon ?



http://v4admin.sportnetwork.net/upload/103/103_0_1529059667.jpg

Re: Testing, testing
Posted by: Brownian Motion (IP Logged)
Date: 09 July, 2020 03:24

I might be misremembering, but those numbers sound similar to that of football before their resumption.

Re: Testing, testing
Posted by: tigersimon (IP Logged)
Date: 09 July, 2020 06:03

PRL considers the results a success and within its expected range, but the 1.2% infection rate is higher than any of the 13 rounds of testing carried out in football for the restart of the Premier League. The first round of Premier League testing saw six positive results from 740 tests.

[www.theguardian.com]

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 08:09

Quote:
tigersimon
PRL considers the results a success and within its expected range, but the 1.2% infection rate is higher than any of the 13 rounds of testing carried out in football for the restart of the Premier League. The first round of Premier League testing saw six positive results from 740 tests.
[www.theguardian.com]
But what is the operational false positive rate?



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.

Re: Testing, testing
Posted by: Yorkie (IP Logged)
Date: 09 July, 2020 08:49

One of the problems from the get go with this Covid virus has been the very high numbers of false positives and negatives amongst NHS staff. A lot of staff were at home self isolating when they didn't need to be.

Testing in football has been costing millions and continues to do so. Wonder who is picking up the tab in rugby?



http://www.jakehowlett.com/tuckshop/wrappers/chocolate/plain/yorkie-nutter.jpg

Re: Testing, testing
Posted by: Yorkie (IP Logged)
Date: 09 July, 2020 08:50

I wonder if anyone in rugby has remembered to test the referees and touch judges?



http://www.jakehowlett.com/tuckshop/wrappers/chocolate/plain/yorkie-nutter.jpg

Re: Testing, testing
Posted by: SK 88 (IP Logged)
Date: 09 July, 2020 09:21

Quote:
harlequinade
I wonder if anyone has read this article?
gov.uk
there is a very serious issue here (not just for sports)
When prevalence is so low then the false positive rate when testing symptom-less subjects is a big problem.
It is known as "The Base Rate Fallacy" for those who want to explore it further!!

Haven't read the full thing but there was a good talk on the BBC's more or less podcast about the idea/issue.
Basically you should really have two tests and only feel sure about the result if both come back the same. If you have mixed results you should go for third test.

Re: Testing, testing
Posted by: Dreadnought (IP Logged)
Date: 09 July, 2020 09:31

Quote:
Yorkie
One of the problems from the get go with this Covid virus has been the very high numbers of false positives and negatives amongst NHS staff. A lot of staff were at home self isolating when they didn't need to be.
Testing in football has been costing millions and continues to do so. Wonder who is picking up the tab in rugby?

I believe its the clubs.

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 09:45

FPM

Quote:
A test which has a sensitivity and specificity of 90% may be useful when there is a high prevalence and the object is to capture most of the true positives. If 50 of a population of 100 are positive, this test will detect 45 of them and wrongly indicate 5 as negative, but will also give 10 false positives. Its Positive Predictive Value (PPV) is therefore 45/55 = 82%. If, however only 10 in 100 are true positives, it will detect 9 true positives, but still 10 false positives, so its PPV = 9/19 = 47%. Now that it appears that the prevalence of COVID-19 is rather low and falling (reported as 0.1% by the Office of National Statistics on 5th June) the issue of false positives may become a real problem.

It may indeed!!!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 11:27

[url=https://www.leicester.gov.uk/media/186760/leicester-in-lockdown-july-2020.pdf
FFS]Leicester Mayor[/url]
This government couldn't run a whelk stall!!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.

Re: Testing, testing
Posted by: Brownian Motion (IP Logged)
Date: 09 July, 2020 11:30

That's not true, they absolutely could.

Very badly.

Re: Testing, testing
Posted by: Tiggs (IP Logged)
Date: 09 July, 2020 11:47

Worcester are another club with confirmed positive tests.



http://v4admin.sportnetwork.net/upload/103/103_0_1529059667.jpg

Re: Testing, testing
Posted by: Tom Paine (IP Logged)
Date: 09 July, 2020 11:56

As the tests are due to continue before the league is re-continued, what level of positive testing would cause it to be delayed? 5 per club? You could imagine that some clubs might not be able to fulfil a fixture. And what happens then? Soccer seems ok at the moment, but they don't have scrums and rucks.

Re: Testing, testing
Posted by: Rich W (IP Logged)
Date: 09 July, 2020 12:25

Scrums and rucks are only a problem if there is contamination in the player group. If players are tested adequately to prove they aren't contaminated and then isolated to prevent exposure it's not an issue.



...

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 12:34

Quote:
Tiggs
10 test positive, with one at Saints and more than one at Sarries, an unknown number at Quin's, and others not mentioned.
That is out of just 804 tests, and before contact training.
Doesn't look good for a return to playing soon ?

The probability of any one of those 10 positive tests actually being due to having the virus is much less than 50%!
Bayes would be spinning in his grave!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 12:38

Quote:
SK 88
Quote:
harlequinade
I wonder if anyone has read this article?
gov.uk
there is a very serious issue here (not just for sports)
When prevalence is so low then the false positive rate when testing symptom-less subjects is a big problem.
It is known as "The Base Rate Fallacy" for those who want to explore it further!!

Haven't read the full thing but there was a good talk on the BBC's more or less podcast about the idea/issue.
Basically you should really have two tests and only feel sure about the result if both come back the same. If you have mixed results you should go for third test.

Exactly right! Preferably from two different testers, using different tests, analysed at different labs!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.



Edited 1 time(s). Last edit at 09/07/2020 12:39 by harlequinade.

Re: Testing, testing
Posted by: harlequinade (IP Logged)
Date: 09 July, 2020 13:40

FDA
Hope it's not this one we are using!
Quote:
The U.S. Food and Drug Administration (FDA) is alerting clinical laboratory staff and health care providers of an increased risk of a false positive result with BD SARS-CoV-2 Reagents for the BD Max System test. In one study, the manufacturer found approximately three percent (3%) of results were false positive results

With those results the probability of a positive test being actually a covid infection with 10 out of 800 testing positive and an actual prevalence of .4% would be about 0.14! i.e 0 or 1 of the 10 with 10 or 9 being non infected!



Life is short,
and art long,
opportunity fleeting,
experimentations perilous,
and judgment difficult.



Edited 1 time(s). Last edit at 09/07/2020 13:43 by harlequinade.

Re: Testing, testing
Posted by: Sara'sman (IP Logged)
Date: 09 July, 2020 14:49

Have you got that right harley? (If the false positive rate means the percentage of tests that give an incorrect positive test then of 800 tests we would expect 3% x 800 = 24 incorrect positives. This would be an incorrect understanding of false positive I believe.)

I understand it to mean the percentage of positive tests that are incorrect. Since there were 10 positives, each of which has a 0.03 chance of being false, the expectation is that 10 x 0.03 = 0.3 (i.e. most probably none*) of them are false positives irrespective of the background rate (which we don't know for the specific population being tested, only an old estimate for the wider population which would appear to be too low here - 10/800 = 1.25% ).


* P(none are false positives) = 0.97^10 = 0.737...
P (one is false +ve) = 10 x 0.97^9 x 0.03 = 0.228...

P(more than 1 is false +ve) = 1 - 0.737 - 0.228 = 0.035

Current Page: 1 of 2
Sorry, only registered users may post in this forum.
We record all IP addresses on the Sportnetwork message boards which may be required by the authorities in case of defamatory or abusive comment. We seek to monitor the Message Boards at regular intervals. We do not associate Sportnetwork with any of the comments and do not take responsibility for any statements or opinions expressed on the Message Boards. If you have any cause for concern over any material posted here please let us know as soon as possible by e-mailing abuse@sportnetwork.net