Pushing all manners of unreliable tests will makes matters worse for everyone.
Any test will need a very high degree of reliability or you’ll end up with large numbers of people being quarantined for nothing or, worse, large numbers of people with the virus allowed to roam free as they believe they are not carrying it.
The other issue is that we don't know what concentration of antibodies is required for immunity. We know these things for other diseases, like influenza, chickenpox, etc. We have no point of reference, so we can only test for the presence of antibodies.
I think antibody tests are still likely to be useful, especially in collecting data on the pervasiveness of the disease and getting information to find out what threshold immunity occurs at. The messaging around them is rife for misuse, though.
Everyone is looking for a silver bullet, but all we can do right now is the long, slog of science to get to a place where it's truly safe to try to return to a semblance of normalcy.
Both my spouse and I had COVID. I say probably because we both showed the expected moderate symptoms and we both did the Roche swab test for COVID. I came back positive. My spouse, with the same symptoms and who sleeps beside me every night, came back negative. Doctor just shrugged his shoulders and said "Yeah, it seems like if you have mild or moderate symptoms, the tests are only about 60% accurate." and just worked on the assumption we both had COVID for his suggested response.
Later on, we did a blood test at local university and we both came back with positive for the antibodies. So yeah Roche needs to address their own tire fire of a test at some point.
Not in this case. My brother works for Roche and is involved in producing the tests. He told me that all tests, except the ones from Abbott, are very not accurate at this moment.
Hearsay of an anonymous internet identity is the best you can get at this point in time. Once the tests are out in May there will be public available data.
Proportionality frequently seems to escape journalists, why be satisfied with reports being confined to the qualitative and non-quantified realm? Give us some background please. In this molecular diagnostics domain what are typical figures for sensitivity and specificity? FDA lays down requirements for such things right? Anyone know off-hand what percentages are required for a diagnostic testing product to be released? For these tests in question how far off from those marks are we exactly?
There is no "typical" I'm afraid. Whether a test is useful or not depends on error rates, priors, and application of the result.
For example, consider this scenario:
- Virus has R0 of 2.5
- the test for the current infection (i.e. not antibody) is cheap and abundant
- the test has 20% false positives
- the test has 20% false negatives
- Application: test every single person and confine everyone who tested positive to their homes, releasing the rest. Repeat weekly. Take no other action.
Result #1: 20% of the population are in isolation. 20% of your economy is stalled, rather than 100%.
Result #2: 1 in 5 infected will go undetected. Still 4 out of 5 are isolated, reducing the number of infected out there by a factor of 5, therefore your R0 drops from 2.5 to 0.5 The number of infected people on the street gets cut in half every week. Epidemic fizzles out.
So even low-precision tests are useful. What is useless is tests that do not have a reliable metric for false positive / negative. Which is what many of the AB tests are.
"Result #1: 20% of the population are in isolation. 20% of your economy is stalled, rather than 100%."
This bugs me, because in this hypothetical, you're implying something as a point of comparison which is nothing like reality. 100% of the population is not in isolation - the only people who are in isolation are those who have had such severe symptoms they've been tested and it came back positive, or they're really obviously linked to such a person. And obviously 100% of the economy is not stalled; it may not be precisely clear what the impact is so far, but people are talking about single digit GDP percentage point declines. If you frame that as the worst economic news since the great recession, or put it in context with the job losses, it's pretty bad, but it clearly could be ten times worse and it's not.
I get that maybe you meant it as just an example and specifics aren't important to your point about statistics, but I feel like I've read similar posts to yours that kind of get the nonsensical scenario out there, that we've shut down "100%" to where people kind of get used to it even though it's not reality.
I don't feel that makes a difference to what I just wrote. But I can do some very rough arithmetic along those lines to see what the decline would have to be.
The GDP figure just reported is -4.8%. Based on what I recall, the inflection point was about halfway through March. Friday the 13th is when the state government in NY finally said anyone who can, work from home. That's 0.5/3 months or ~17% of the quarter I'd assign to "shutdown".
0.83 * 1 + .17 * x = .952
...I don't trust myself to do high school algebra, so I asked Wolfram Alpha and it said x = 72%. Ok, so the reported figure of nearly -5% probably equates to a little over a quarter of the economy missing.
I don't think I need to concede my point about a 100% stoppage not happening.
The larger point stands it’s just ‘but people are talking about single digit GDP percentage point declines‘ that I was correcting. That said, Pennsylvania and several other states waited until April to order a shutdown, but the observed GDP decline was annualizing a ~1% though there was growth in the ready of Q1.
Long story short, that 4.8% is absolutely worthless.
The bit you quote from me seems strictly accurate; by single digit I mean < 10%. That is what the news is reporting. It is factual, and my inference that the economy is not shut down hasn't been questioned.
Saying that the difference is larger when you consider only part of the quarter is correct too, but 4.8% is not "absolutely worthless", it just needs to be interpreted properly.
As in my previous comment, you can approximately derive the actual amount of decline, which is a fraction of a complete shutdown.
By absolutely worthless I mean it’s a meaningless calculation. They take the actual change averaged out over a quarter, and then assume 4 more quarters will have exactly the same thing happen.
It’s a common calculation used to make quarterly numbers seem more important, but it’s at best misleading if not actively deceptive.
Wait, wait, wait. Nothing is "meaningless" if it contains information. And "misleading" depends entirely on context.
It sounds as though you are suggesting I made an error that increases the apparent size of the shutdown, meaning it is actually smaller and my claim is stronger than I thought.
If the figures are annualized (I checked* and I think you're right) then it improves my original point - the 4.8% decline becomes 1.2% un-annualized, and the normal trend of +2% becomes +0.5%.
The equation should then be something like .167 * x + .833 * 1.005 = .988, "x" being the percentage of the economy active in the last half month, or about 90%.
I'm confident that there is information in the reported figure and that no reasonable calculation can show the economy was shut down completely.
You’re ignoring information that you disagree with. Yep, of the multiple errors in your calculation, one of them lowers the estimate. But, I never said anything about a 100% shutdown just that single digit comment.
Going in the other direction, picking the earliest possible starting date underestimates the impact as does ignoring panic buying. Layoffs where also not instantaneous, and people’s final paychecks are delayed etc. All of this is going to show up in Q2 numbers even if many states are scaling back their shutdowns.
As to being a meaningless calculation, you’re describing a reversible calculation not a useful one. I can type a message in ROT13 and the result contains the same content, that does not make me doing the ROT13 useful.
"You’re ignoring information that you disagree with"
You're the one saying information is "meaningless", and at the same time I don't see any alternative data that you've provided. You're just making general statements that sound to me like the fallacy that imprecision means no information.
In your first reponse to me, you wrote:
"It requires a very large decline to average out to ‘just’ 1%"
So, "very large" is subjective, but I don't think 10% is "very large" in the context of people talking about 100% of the economy being down.
It’s imprecise enough that you’re better using other means to estimate the decline. I am between 1cm and 1 mile tall, is true but does not convey new information.
Similarly without knowing how fast was the economy was growing or shrinking before the decline, the decline hit, when peak decline hit, it’s impossible to say how bad things where at the end of the quarter beyond well it’s worse. I mean presumably when news of the outbreak hit but before the shutdown there was some effect, but I don’t know if it was a net positive or negative.
If you want numbers I would say 10+x larger is objectively a very large decline relative to 1%. Anyone talking about a 100% shutdown while still buying food is being using hyperbolic or simply does not understand what their words mean. It’s at best symbolically true in that net wealth is being destroyed so the engine of human progress has shut down.
So interesting, so even with inaccurate tests so long as we're dealing with reliable metrics backing those tests up then the degree of actual accuracy that intersects with the nominal accuracy is enough to carry out the compounding with and effect targeted quarantines with. Probability products stack up quick. Hope that makes some bit of sense.
So how statistically independent is the error between serological tests? If we make 5 tests on the same blood sample and go with 3 or more out of 5 rule, would that help with FP and TP?
I agree, the people who want “the red tape eliminated — lives are at stake” are nuts. Garbage data is garbage data and getting it sooner doesn’t help.
False negatives can cause someone contagious or sick to go out and infect others; false positives can cause unnecessary treatment and take up hospital resources that should have been spent on actual patients.
From what I gather a false positive for an antigen rtPCR is essentially impossible. The primers are extremely specific and can't find something that isn't there.
A false positive for an antibody test is unlikely to take up hospital resources. They admit people to the hospital for symptoms like dyspnea/hypoxia. Not because the patient tested positive on either the antibody or antigen test. The danger in a false positive for an antibody test IgG or IgM, means gives the patient a false sense of security that they've already gotten the virus and are thus immune in the short to medium future.
>a false positive for an antigen rtPCR is essentially impossiblee. The primers are extremely specific and can't find something that isn't there.
I read somewhere that among the reasons for a false positive would be cross-contamination among samples.
Just because the primers find something in the sample, doesn't mean that that something isn't in fact merely a bit of cross-contamination from another, true positive, sample.
That looked like some really sloppy lab technique, and I hope that's not how it is really done in practice. If real tests are done by hand like this, with distractions, open air, and no mask on the technicians, it's easy to imagine false positives.
I believed it was based on false negatives in previous PCR tests?
It's also a question of understanding what the test actually means. The test doesn't (and can't) claim "this patient is cured" but only "when analyzing this specific sample taken from this patient, no significant trace of virus could be confirmed."
No, the patients were cured but later portions of the virus were again detected. These portions turned out to be inactive.
Of course it is possible to define the test in such a way it is 100% effective. This removes the relation to the Covid-19 disease though so then the test is useless.
chevy calls fords new car garbage.
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