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Preliminary test results suggest 21% of NYC residents have Covid antibodies

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Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#571

Post by gwright »

koheripbal wrote: post #546
mannykannot wrote: post #499

Earlier quoted context omitted.

NYC is not suburbia. I believe a higher percentage are still working outside of their homes (and, in many cases, that also means travelling on public transport), and a smaller percentage have the financial and transport resources to significantly reduce the frequency of their shopping trips. Apartment living means a greater exposure to your neighbors whenever you do enter or exit. The sampling in NYC, while far from…

As a (40-something) NYC resident, I don't believe that is accurate. Half of the people I know are working from home and stocked up on 1-2 months of food at the outset of this. The other half left the city and are now staying with friends/family in other states or have rented homes elsewhere. Those that did stay and still need food (ie produce) are having it delivered. People who are shopping in stores are absolutely…

> Half of the people I know are working from home and stocked up on 1-2 months of food at the outset of this.

This surprises me if for no other reason than it takes a lot of space to store 1-2 months of food. Might be true, but is certainly different than what is going on in suburban Connecticut based on my social network.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#572

Post by [deleted] »

ineedasername wrote: post #560
greedo wrote: post #501

Earlier quoted context omitted.

The amount of testing for influenza is nugatory. Most of the CDC data is collected by surveys, not tests.

There are near instant tests for flue in most every urgent care center I've been to (easier and faster than getting a dr appt.) Whenever I have gone or brought my kids when sick, they perform the test to rule out any potential need for antibiotics. When I asked, they said it's systematically reported to the the CDC as part of their flu surveillance system, whether positive or negative. That surveillance network is si…

[deleted]

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#573

Post by mlthoughts2018 »

capkutay wrote: post #558
Karrot_Kream wrote: post #401

Earlier quoted context omitted.

> Sure all of these studies are potentially flawed but they're all generally pointing in the same direction That's unfortunately not the way statistics works. Combining multiple bad tests just makes the results incorrect or highly uncertain; the devil often is in the details. The Stanford/Santa Clara County study is a good example of how the details can really undermine a study. Things do indeed seem to be converging…

OP's whole point is it's not a good sample because people were recruited while grocery shopping...I can't think of a more tech industry-oriented view of the world; most people work from home on zoom and use instacart right?? No. I'd expect people who order deliveries online and can do their entire job on Zoom/slack all day to be a minority to the point where including them in the study would be covered in a sampling…

You’re completely missing the point. The selection effects would be things like able-bodied / non-immunocompromised / already-recovered people being selected way higher, which would inflate the apparent infected population size estimate and underestimate the death rate among those infected.

This is not some snooty tech point of view - this kind of flaw in statistical studies matters a lot. The more important the policy implications are, the more important the validity of statistical methods.

It’s anything but parochial.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#574

Post by qqqwerty »

timr wrote: post #495
zamfi wrote: post #427

Earlier quoted context omitted.

> Are all three methods flawed in some way? Sure. They're not just all flawed in some way -- along at least one dimension they are flawed in the same way , that is, they all have a biased sample of the population that seems more likely to be infected than a true random sample. So, sure, they're "created differently", i.e., they're not all facebook ads, or grocery stores, but all those methods bias towards higher infe…

These studies have completely different methodologies, and the only way you can plausibly call them similar is by arguing that anyone willing to get serological testing is substantially more likely to be infected than those who are not. That's little more than a fancy way of disregarding any testing result you don't happen to like. We've been systematically biasing toward testing the old and infected for months now.…

Anyone worth arguing with acknowledges the limitations of the PCR testing. You are essentially suggesting that we ignore the limitations and biases of these serological surveys. If a handful of internet denizens can quickly point out methodological flaws, maybe the researches should try to address or account for those. I fully understand the urgency of the matter, and that urgency can lead to mistakes. But these studies are going to be used in policy making and could potentially impact millions of lives. The difference between 1% and 0.5% is huge, that is over 1.5 million in the US. And powerful people are trying to use these studies to make a case for re-opening the economy. I think it is completely reasonable to push back on these flaws and biases in light of that.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#575

Post by Marsymars »

legulere wrote: post #277
DeonPenny wrote: post #73

Earlier quoted context omitted.

We'd also need to make the decsision to continue a lockdown over a virus with a 99.5% survival rate or not. Seeing at the flu has a 99.9% survival rate does it make sense to destroy the economy over that.

Stating the survival rate really hides how there is around an order of magnitude difference in the death rate. And that ignoring that while immunity towards various types of influenza is widespread, there is no previous immunity against COVID-19 apart from a handful of people that had SARS or MERS before.

I wouldn't expect SARS-CoV-2 immunity from a previous MERS infection, AFAIK their similarity is in their severity of outcomes, not in the immune responses.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#576

Post by Terretta »

usaar333 wrote: post #407
t2riRXawYxLGGYb wrote: post #326

Earlier quoted context omitted.

This was my thought exactly. Some of my friends in the Bay area got COVID-19 (confirmed positive tests) after quarantining for over two weeks at home and taking all of the precautions. The only place they had been was the grocery store, so they suspect that they got it there.

Are they not taking public transit? Your friends must be some of the most unlucky people ever. The Bay Area has had under 3k cases since the start of April outside group living settings (nursing homes, homeless shelters, etc.). That's ~1/2000 chance of getting covid from anywhere outside.

Remember that’s not a count of cases. That’s a count of the under 3000 people that came up positive after permitted to take a limited availability test.

Take total case deaths, divide by CFR, that’s how many likely total infected there were 3 weeks ago, and then compound daily by the daily spread rate to find how many likely today.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#577

Post by hsitz »

ccleve wrote: post #17

This study doesn't appear to suffer from the same methodology problems as the Stanford study of a few days ago. In that study, they recruited people through Facebook, and reported an infection rate that was low enough that it could have been caused by false positives. Here, it's closer to a random sample, but more importantly it shows really high rates. Those rates overwhelm any error due to false positives. Also, it…

> Here, it's closer to a random sample, but more importantly it shows really high rates. Those rates overwhelm any error due to false positives.

I'm not seeing that, at least not from what I've seen. Whether false positives skew results significantly is highly dependent on how accurate the antibody test they used is (in addition to how large a subset of the population is positive).

This guy has an interesting visual tool that helps you to see how much a study could be affected. [1] Also, he says "Here's an interesting relationship. When a test with 95% sensitivity and 95% specificity is applied to a population with Do we know the sensitivity and specificity accuracies for the antibody tests used in NY?

You'd like to think they know what they're doing. But this Bayesian stuff can be tricky, especially if they're rushing something through (esp. regarding testing of accuracy of the antibody tests themselves). And the California studies, although they seem to have some competent people behind them, seem to inflate/exaggerate the lower bound of uncertainty in their projection. [2]

[1] https://sites.google.com/view/tgmteststat/home

[2] https://statmodeling.stat.columbia.edu/2020/04/19/fatal-flaw...

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#578

Post by timr »

zamfi wrote: post #570
timr wrote: post #495

Earlier quoted context omitted.

These studies have completely different methodologies, and the only way you can plausibly call them similar is by arguing that anyone willing to get serological testing is substantially more likely to be infected than those who are not. That's little more than a fancy way of disregarding any testing result you don't happen to like. We've been systematically biasing toward testing the old and infected for months now.…

> arguing that anyone willing to get serological testing is substantially more likely to be infected than those who are not. Yes, which is clearly true, no? > That's little more than a fancy way of disregarding any testing result you don't happen to like. We all have biases. I'm not sure how pointing out that adverse selection is a thing, though, is a bias. Any stats can be quibbled with, and I have no personal skin…

"Yes, which is clearly true, no?"

No. As far as I can tell, approximately 100% of people in New York want to be tested, for many different reasons. You're assuming something and projecting it as truth.

"These studies would ideally be true random samples so that we can know what the true infection rate is."

But by your own logic, there can be no "random sample"...we can't tie people down and force them to be tested, so we have to ask them. This means we're back to the self-selection problem that apparently ruins the sample.

The truth is, the New York study did pretty much what we always do to get a random sample: asked a bunch of people at random to participate in the program.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#579

Post by timr »

qqqwerty wrote: post #574
timr wrote: post #495

Earlier quoted context omitted.

These studies have completely different methodologies, and the only way you can plausibly call them similar is by arguing that anyone willing to get serological testing is substantially more likely to be infected than those who are not. That's little more than a fancy way of disregarding any testing result you don't happen to like. We've been systematically biasing toward testing the old and infected for months now.…

Anyone worth arguing with acknowledges the limitations of the PCR testing. You are essentially suggesting that we ignore the limitations and biases of these serological surveys. If a handful of internet denizens can quickly point out methodological flaws, maybe the researches should try to address or account for those. I fully understand the urgency of the matter, and that urgency can lead to mistakes. But these stud…

"You are essentially suggesting that we ignore the limitations and biases of these serological surveys."

I am not. I am suggesting that you are preferring a rate based on an even more biased method, because the method yields a bigger number.

"If a handful of internet denizens can quickly point out methodological flaws, maybe the researches should try to address or account for those."

If a handful of internet denizens can quickly point out "methodological flaws", it usually means that the "methodological flaws" they have discovered are well-known and accounted for. In this particular case, sample bias is not a new statistical phenomenon, and we've been doing serological surveys for a long time.

Re: Preliminary test results suggest 21% of NYC residents have Covid antibodies

#580

Post by [deleted] »

koheripbal wrote: post #546
mannykannot wrote: post #499

Earlier quoted context omitted.

NYC is not suburbia. I believe a higher percentage are still working outside of their homes (and, in many cases, that also means travelling on public transport), and a smaller percentage have the financial and transport resources to significantly reduce the frequency of their shopping trips. Apartment living means a greater exposure to your neighbors whenever you do enter or exit. The sampling in NYC, while far from…

As a (40-something) NYC resident, I don't believe that is accurate. Half of the people I know are working from home and stocked up on 1-2 months of food at the outset of this. The other half left the city and are now staying with friends/family in other states or have rented homes elsewhere. Those that did stay and still need food (ie produce) are having it delivered. People who are shopping in stores are absolutely…

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