Utilico Insights - Jacqueline Broers assesses why Vietnam could be the darling of Asia for investors. Watch the full video here.
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@CautiousOptimist - I hear you ! Why oh Why do they need to use the same terms in different contexts !?
When I was involved with drafting the guidelines - each guideline had it's own glossary to define terms. After a few years the same term cropped up over and over in different guidelines glossaries with just subtle differences. Eventually, the job of gathering all the guidelines glossary entries together was given to the group defining the Common Technical Document. They struggled for so long that in al lot of cases they just duplicated glossary entries in the end to keep everyone happy.
This reminds me of that. - Anyway - I have read and re-read your description and explanation and I find myself in complete agreement with your writing and conclusions so somewhere along the line - how ever our wires got crossed - right or wrong I think I agree with what you described.
Ophidian
Hi Ophidian, thanks for taking the time to check it and reply. Indeed, not knowing the finer nuances of the terms in other settings, all I am going on is the clinical definitions, as described in Alistair’s video.
Perhaps a phrase in the explanation you cited that could muddy the waters for some is “actual ... results”. “Actual positives” (P, or TP+FN) is distinct from “positive results” (TP+FP). Hence, SENS = TP/P = TP/(TP+FN).
I think we’re on the same page in the end. But if this can cause differences in opinion among us scientists, even after watching Al’s excellent video, you can see why grappling with this causes problems for most of the general public!
Have a good week ahead.
@CautiousOptimist - to move on:
Negative Predictive Value NPV = TN/(TN + FN) so since a false Negative result is a negative result that SHOULD register as a positive I accept that the Sensitivity of the test has a bearing on the NPV.
Crikey this is tough for a sunday evening.
Ophidian
@Cautious Optimist - you've sent me scurrying back to the definitions. I have to go careful because to me sensitivity, selectivity and specificity are terms used to describe the suitability of an Analytical method and so the fact that terms are also used in a clinical sense often catches me out. However - not here I hope.
The clinical sensitivity of a test is defined as the ratio of True positive results (TP) to the actual number of positive results in the group being tested (P) SENS = TP/P
The clinical Specificity of a test is defined as the ratio of True Negative results (TN) to the actual number of negative results in the group being tested (N) SPEC = TN/N
Thee is a very good summary slide in the most recent Avacta video
https://avacta.wistia.com/medias/wls4u1wqgi?hss_channel=tw-2279270671
So no - I didn't mean to type sensitivity
Ophidian
Great video Timster, watched it already and confirms my points. What isn’t written on the slide of definitions in the first minute, but leads a lot of people to confusion if you don’t grasp it, is:
P=TP+FN
N=TN+FP
Watch this all is revealed by big Al
https://avacta.com/how-diagnostic-test-performance-is-measured/
Even I understood it..
Ophidian, when you said “A HIGH specificity gives a Low number of False negatives and so hence - a HIGH NPV (Negative Predictive Value)”.
Did you mean to type sensitivity here?
My reasoning, apologies if it’s like teaching you to suck eggs, but might be useful for others... If you’ve actually got the virus, sensitivity is about whether the test detects it or not, and so determines the fraction of actual positives that are either detected as true positives or not detected, I.e. read as false negatives. Conversely, specificity controls rates of true negatives and false positives for the actual negatives.
Negative Predicitvie Value (NPV) is a function of false negatives, true negatives and prevalence, so specificity and sensitivity both have an impact on it, albeit sensitivity is more important.
NPV will always be between (1 minus prevalence) and 1 - otherwise you wouldn’t use the test, so a high number for NPV is to be expected for low prevalence, but you want the test to push it closer to 1.
Therefore I think NPV doesn’t tell you much for low prevalence settings, e.g. population screening. Most important to remember is: high sensitivity reduces false negatives, which will help to detect and keep more infected people isolated. High specificity reduces false positives, meaning fewer people have to isolate for nothing while awaiting PCR confirmation, and less strain on the test and trace system.
CaptainStainley that is a beautiful part of the world! Been up there many times!
Fair enough, I’ll leave it to you to point out each one. I’m gambling on 100% of them, if by a miracle I miss out so be it - the RNSs are all that is important.
Yes! What a result. Even better if he went to GDR full time to upset their board was not nice there today. Just wish they would stop trying to diminish our company name buy changing the v to a w just to annoy people.
Bet I get a response though ;-) Translucent filter....
CS, this was a suggestion made by CO yesterday and was a good one. His mounted lordship has latched on to that in the hopes he’ll be able to say it was his idea to soothe his fragile ego. My best advice to you is to put him on ignore, I have as I’m bored on his insane paranoia. All you’ll miss out on is vaguely educated guesswork. The waffly cheerleader has been binned too. Much better board today! Try it, you might like it...
whatever works for you Captain - take your meds and let nurse put you to bed. Don't worry your little intellect over things you can't possibly understand.
@minimil - A hospital only version of the LFD could even encompass the use of additional solvents potentially should that be required allowing for tailored optimisation to Hospital diagnostic use. All in time I suspect. let concentrate on getting the mas market one out first.
Ophidian
Ophidian - I also believe they need two types of LFT. If this is the case then I would have expected a faster drive towards approval/marketing the general population one (as this is the bigger $ earner). If the higher prevalence version requires more time to develop (as implied in latest RNS) why sacrifice sales if the lower prevalence is ready to go? Unless of course the lower prevalence is still not ready.
@PAH00 - without fully understanding the compromises in the affimers per se - I don't think anyone outside the company can really answer that one. I'm not so sure that optimisation necessarily means playing one off against the other. More likely it is favouring one over the other in the mechanics of how the basic chromatography on the strip works. I could see how you might want to speed up the result for example and that might be by changing the viscosity on the strip perhaps which might mean changing the concentration of the affimer which could impact the sensitivity or selectivity more or less.
Just idle speculation as I don't have the necessary data to be able to say.
Just as a thought - who says they only have to produce one LFD. I could easily see one for low prevalence use for general population screening and another one for use in Hospitals and other higher prevalence areas. Why not ?
Ophidian
Just to clear up the question from earlier. A HIGH specificity gives a Low number of False negatives and so hence - a HIGH NPV (Negative Predictive Value) which is what is required for getting the country back on it's feet.
Ophidian
Nope. I've re-watched the relevant bit from this video and specificity is the one to do with false negatives.
I wish you were right, though re: the Indian test.
but it depends to a huge extent on the prevalence of the infection in the population.
Ophidian
If I was paying attention to AS's video last week, it is specificity which is the more important one as it prevents false negatives - i.e. I am sure I haven't got it. False positives (due to that tests low-ish sensitivity) means if it says you have got it, then you're not certain of that, so would have a PCR test to double-check and hey a couple of days of isolation that you don't need won't harm anywhere near as much as (with a false negative) thinking you're safe and infecting loads of people.
sorry - Oops try this link http://sdbiosensor.com/xe/index.php?mid=promotionNews&category=2288&document_srl=16241
Some info on LFT supplier in India - Hopefully AVCT product will at least meet or better this product .
FYI The antigen test — developed by private biotechnology firm SD Biosensor (swab sample from nose ) result in 30 mins
Video/info below
http://timesofindia.indiatimes.com/articleshow/76395986.cms?utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst
http://sdbiosensor.com/xe/index.php?mid=promotionNews&category=2288&document_srl=16241
https://timesofindia.indiatimes.com/india/icmr-gives-nod-to-antigen-based-testing-kit-for-faster-diagnosis/articleshow/76395986.cms