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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.
Meanwhile other people are going out every day, or they know they previously had covid so they consider themselves exempt from shelter in place, or they have a job that requires them to continue heading out to work despite shelter in place (and therefore they have had far more exposure to covid than average).
Can we change the title? Article title is "Nearly a third of 200 blood samples taken in Chelsea show exposure to coronavirus" The sample is clearly not random
>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…
https://abc7news.com/coronavirus-test-free-testing-update-ac...
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.
Earlier quoted context omitted.
Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]: > In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397…
Specificity of 90% seems really low? Does that mean almost 1 in 10 would test positive even if nobody had it?
That would imply the correct rate is closer to 22% than 30%, as of the 64 positives out of 200, we would expect roughly 20 of those to be false positives. (So the remaining 44/200=>22%).
Article says there are 40k residents and 39 deaths.
If 22% of 40k are infected => 8800 infected.
37/8800 implies .42% IFR, broadly consistent with figures elsewhere, especially given that there is a lag time for deaths. (Which will cause the IFR to increase.)
Any bias due to selection etc would basically decrease the denominator on that calculation, increasing the IFR.
(This is all just back of napkin, based on numbers in the article, please check my calculations.)
Can we change the title? Article title is "Nearly a third of 200 blood samples taken in Chelsea show exposure to coronavirus" The sample is clearly not random
Your never going to have a completely random test. Your randomness comes from you picking for an area and the people who chose to do the test. Saying otherwise is being pedantic to your detriment.
Earlier quoted context omitted.
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.
It's worth noting, though, that the natural tendency during an epidemic is for the total number of infections to exceed the herd immunity threshold; I think the phrase to google is 'herd immunity overshoot'.
(It's also worth noting the serious problems with this study, as pointed out by other commenters.)
Can we change the title? Article title is "Nearly a third of 200 blood samples taken in Chelsea show exposure to coronavirus" The sample is clearly not random
Your never going to have a completely random test. Your randomness comes from you picking for an area and the people who chose to do the test. Saying otherwise is being pedantic to your detriment.