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there is only so many times you can rub the lamp !
Ophidian
Thanks Ophidian I knew if I called you'd appear :)
it is also worth pointing out that in the registration context, the requirements are for ANALYTICAL selectivity, specificity and sensitivity NOT Clinical.
Ophidian
I'll give you an example you might relate to better, as you clearly don't have any understanding of the biological or epidemiological merit.
If we're looking for strong investment choices, a punter with high sensitivity and specificity finds ALL the strong investments and never strikes out. That's a Warren Buffett. If you have a high sensitivity and low specificity, you'll throw money at anything that catches your attention, whether or not you should. That's 95% of LSE
And I'm agreeing wholeheartedly with Ophidian, whatever next...
You might see it as a bad result in your profession but back in the real world it's not an issue. I've not seen a decent counter argument yet...
@tomvisual - yes and no. The lab results confirm that the affimers are highly specific to the exact antigen presented by SARV-COV-2 (the spike proteins). To the best of my knowledge they haven't confirmed anything thus far in terms of how well that is picked up from a natural saliva sample, which will have all kinds of other gunk in it, or how well it performs on a test strip. That's the next big RNS, as Cytiva are seeing to that side of things
Specificity is the ability to measure a particular target rather than other similar or related target.
e.g. can we detect COVID19 rather than SARS or MERS – answer yes – 100%
Selectivity is the ability to measure a particular target EVEN IN THE PRESENCE of other similar and related targets
e.g can we detect COVID19 even if the patient also has SARS and MERS – answer irrelevant as for this poor bugger it’s probably too late.
Specificity and selectivity are being used interchangeably here and whilst wrong to do so in this case it really doesn’t matter as we already know from the company that affimers ONLY detect the COVID19
Accuracy is the closeness of a result to a known standard or outcome
As we are only asking a yes no question this is also a bit irrelevant
Sensitivity is the ability to determine Quantitatively between two levels above the limit of detection.
e.g. is it 5,000 units per ml or 10,000 units per ml
Again irrelevant in a yes no scenario – what is important here is the limit of detection.
There is also CLINICAL sensitivity and specificity which are different things.
Clinical Sensitivity is the ability of the test to correctly identify those patients with the disease. A test with 100% sensitivity correctly identifies all patients with the disease.
We will not have 100% clinical sensitivity because the test (no test) can detect the very lowest levels of infection prior to the patient being symptomatic.
Clinical Specificity is the ability of the test to correctly identify those patients without the disease. Therefore, a test with 100% specificity correctly identifies all patients without the disease.
Again – for the same reason as with Clinical sensitivity this will not be 100%
For all reasonable purposes it is the ability to correctly identify “spreaders” of the disease that is important here and with what we know the affimer test has the highest likelihood to be able to do that as it probably has a lower LOD than other similar tests and can identify pre-symptomatic as well as symptomatic patients.
Also – and this is the important bit missed by some others – the likelihood of generating an incorrect positive result is very very low due to the Selectivity and Specificity of the affimers.
Ophidian
Our primary focus is on diagnostics in which the technical benefits of Affimer technology lead to better sensitivity, specificity, speed of development, robustness and security of supply.
The unique properties of Affimer binders can also provide novel competitive advantage. For example, in converting a competition assay into a sandwich format.
From the Avacta website. Don't think the sandwich format is to do with bread.
Hilarious, I'm sure. But this is an entire thread about muppets not understanding the statistics underlying a test. Relevant, wouldn't you say
I'm sure your credibility as a statistical biologist is sound when it comes to statistical biology, but when it comes to investing you are clearly a highly proficient statistical biologist.
No, you're right PL75. I'm only a statistical biologist so I'm sure you know antigens vs antibodies better than I do...
I'm telling you for a fact that any false positive is inherently a bad result, and that means the test doesn't work well. Avacta isn't aiming to create a bad test, it's aiming to take the best the lab can provide and put it in your pocket. If it can't do that, this SP will sink like a stone, because all the short term holders that only know about a COVID19 test will leave in a rush.
I just... can't... understand your perspective here. Is there a sane reason that you think a test producing a high rate of false positives is a good thing?
And yes, FDA approval numbers are a low bar, but it's a competitive market. Having FDA approval means Avacta/Cytiva can sell a test, it doesn't mean anyone would buy it
Outside of the strip they can test for specificity, its needs to be a finished prototype to test for sensitivity
Would Avacta have tested the affimer for sensitivity and specificity and hence accuracy before sending to Cytiva?
Ok, I'll have to answer for you. You don't understand the difference between an antibody and antigen test. False positives are not an issue for an antigen test. All that results in is more people than strictly necessary isolating.
PL75 do you think this company is going to carry on shooting for the moon with a test that has low specificity? We're banking on this test becoming a first choice diagnostic device as it has speed and resource benefits over the gold standard, almost 100% sensitive and specific laboratory tests.
No company or government are going to shift from current testing best practice to Avacta's test if it produces a large number of false positives. That makes it a bad test, and it will never go to market.
If the crucial question is "do i have this virus" and the test isn't sensitive, the answer isn't yes or no, it's Maybe, and that helps absolutely nobody
I'm not sure why posters here seem to have a negative response towards pure statistics. By my reckoning Abdalian's comment is correct and correctly identifies the problem.
The positive out of this is that a) infected persons exhibit high viral load in saliva b) these affimers have already been demonstrated to have an incredibly high specificity per the RNS (even with decoy targets which are very closely related viral 'species') c) this test is for antigens, which has a clear role in infection, whereas antibodies don't seem to have a confirmed role in long term immunity. All the right pieces are in all the right holes.
Just please be aware that when someone presents statistics and you 'doubt' them, you lose all credibility as an informed voice
Surely this is a joke?
Answer it then.
Oh God not this again..... OPHIDIAN where are you???
"Why is a false positive an issue for an antigen test?" - surely this is a joke?
"If one person in the UK is infected and you test all 65M and get 2 positive results, one true and one false, that does not mean the test has produced 50% false positive results" - this is what positive predictive value is. It means "how likely is my positive to be really positive". Abdalian's analysis is correct based on the numbers they provided. For the numbers you provided the specificity would be 99.99999985%, which again, agrees with the "specificity of the test needs to be pretty much 100%" as stated below
It also simply results in 2 rather than 1 person isolating, which isn’t a concern.
Abdilian. Lets make the numbers extreme. If one person in the UK is infected and you test all 65M and get 2 positive results, one true and one false, that does not mean the test has produced 50% false positive results
“false positive, unfortunately rendering it useless”
Why is a false positive an issue for an antigen test?
Just because you do not understand it does not mean that it is bovine by-product.
Jees - another one.