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Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

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Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#11

Post by wtvanhest »

This is another irresponsible headline.

I cannot read the article, so correct me if I am wrong, but if what others said is true...

It was not random because they didn't randomly select people, they let people self-select!

If they gave the total number of people who took the test, and total number of people asked, you could at least get a range.

Of course, that range would still be biased to people who are walking around during a time when they should be sheltering in place.

At best, 30% of people who were offered a covid antibody test in public had antibodies.

I think its safe to say that journalists have a responsibility to get the headlines right on this topic or they risk causing a lot of people to make bad decisions after hearing that 30% of people already have this disease. There is a real human cost of this click-bait, and it will be deaths.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#12

Post by jwegan »

trav4225 wrote: post #7

Hmm, I wonder if they attempt to control for bias. It sounds as though they were asking random passersby if they wanted a COVID-19 antibody test. If so, it seems that the sample group could be biased toward including more people who suspected that they may have been infected (previously or currently) than a truly random sample.

Also biased because they are sampling people who are out and about. People who are out and about likely come into contact with more people than people who are staying at home and rarely going out.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#13

Post by powvans »

scythe wrote: post #6

A third of a random sample taken in Chelsea, Massachusetts : https://en.wikipedia.org/wiki/Chelsea,_Massachusetts >Chelsea is [...] directly across the Mystic River from the city of Boston. [...] It is also the second most densely populated city in Massachusetts behind Somerville. A random sample in a highly affected and extremely dense area is not a model for the whole state.

As soon as I saw this study I Googled Chelsea Mass and in the first few results was an article about how it has been hit hard by the virus. From the article:

> “Chelsea is suffering in this pandemic,” City Manager Tom Ambrosino told WBZ News. “We have, as far as I can determine, the highest infection rate in the Commonwealth.” [1]

With that information the takeaway should be that in the areas with the highest rate of infection we are seeing as much as 30% of the population with antibodies. That's great and an encouraging statistic that seems to indicate the percentage of mild or asymptomatic cases is much higher than originally believed. It does not mean that we are close to herd immunity everywhere. We need randomized testing in many many more communities across the country in order to get the full picture.

[1] https://www.boston.com/news/local-news/2020/04/10/chelsea-ma...

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#14

Post by majormajor »

Exmoor wrote: post #10

>Nearly one third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, a startling indication of how widespread infections have been in the densely populated city. >The doctors used a diagnostic device made by BioMedomics, of Morrisville, N.C., to analyze drops of blood. It resembled an over-the-counter pregnancy test and generated…

This doesn't seem that random - it is sampling from people on the street. So it's going to miss people who aren't going out onto the street. And people who are going out are more likely to catch something than those who aren't.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#15

Post by lubujackson »

scythe wrote: post #6

A third of a random sample taken in Chelsea, Massachusetts : https://en.wikipedia.org/wiki/Chelsea,_Massachusetts >Chelsea is [...] directly across the Mystic River from the city of Boston. [...] It is also the second most densely populated city in Massachusetts behind Somerville. A random sample in a highly affected and extremely dense area is not a model for the whole state.

Chelsea is literally the hardest hit town in MA: https://www.nbcboston.com/news/local/the-20-communities-with...

I have some natural doubts over all these antibody tests that indicate herd immunity while covering up major flaws...

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#16

Post by Exmoor »

point78 wrote: post #4

So halfway to herd immunity?

It was discussed in another thread that I'll try to dig up, but the percentage of the population required to reach herd immunity goes up the more contagious a virus is. If way more people are infected then we think, then it points to some of the higher R0 estimates being accurate and would therefore require a much higher portion of the population to be immune before we reach herd immunity.

Edit: Here it is: https://news.ycombinator.com/item?id=22819057

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#17

Post by james_s_tayler »

Exmoor wrote: post #16
point78 wrote: post #4

So halfway to herd immunity?

It was discussed in another thread that I'll try to dig up, but the percentage of the population required to reach herd immunity goes up the more contagious a virus is. If way more people are infected then we think, then it points to some of the higher R0 estimates being accurate and would therefore require a much higher portion of the population to be immune before we reach herd immunity. Edit: Here it is: https://n…

My understanding is it's (R0 - 1)/R0

So if R0 is 4 then 3/4 of the population is required to be immune before herd immunity kicks in.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#19

Post by bitcurious »

jwegan wrote: post #12
trav4225 wrote: post #7

Hmm, I wonder if they attempt to control for bias. It sounds as though they were asking random passersby if they wanted a COVID-19 antibody test. If so, it seems that the sample group could be biased toward including more people who suspected that they may have been infected (previously or currently) than a truly random sample.

Also biased because they are sampling people who are out and about. People who are out and about likely come into contact with more people than people who are staying at home and rarely going out.

Out, about, and willing to speak to a stranger, which I think is the biggest bias. Pretty much everyone I know goes on the occasional walk, but we all stay the fuck away from other people.
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