6 ms·
"Preliminary test results suggest 21% of NYC residents have Covid antibodies" Should be re-written as: "Preliminary test results suggest 21% of of people appr
by wtvanhest 6y ago
"Preliminary test results suggest 21% of NYC residents have Covid antibodies"
Should be re-written as:
"Preliminary test results suggest 21% of of people approached in a crowded grocery store and who would agree to give blood have Covid antibodies"
All of these tests suffer the same sample bias, and that sample bias is massive.
People who are already in a grocery store (risky behavior), who are willing to give a blood sample (believes they may have been previously exposed) are not the same as people who are leaving their house only for very limited purposes and ordering food online.
If we assume that the % of people shopping in grocery stores and willing to take the test are in risk group A, and the people not shopping are in risk group B. We can run the following quick analysis.
First, assume risk group A is 5 times as likely to have had COVID than Risk group B (but plug any assumption in there necessary)
Then assume that risk group A is only 10% of the population, then rerun the numbers as follows:
For every 100 people in risk group A who tested, 21 were positive.
Risk group A is 100 people, and risk group B is 900.
Risk group A's 100 were 21 prior positive.
Risk group B's 900 could be estimated that 4.2 people per 100 were positive, so in total of the 900 people 37.8 were positive.
21+37.8 = 59 people of 1000, or 5.8%.
Plug any numbers you want in the analysis, but the assumptions drive huge variability in the % of New Yorkers infected. Without a less biased sample, we really don't know much other than that way less than 21% of New Yorkers have anti-bodies.
- walterbell 6y ago> Preliminary test results suggest 21% of of people approached in a crowded grocery store and who would agree to give blood have Covid antibodies Would be useful to know how many deaths from the same zip codes are people who visited crowded grocery stores.
- mannykannot 6y agoNYC 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 ideal, may therefore be better than the other regions, in that shopping behaviour may not be as dominant a risk factor as you suppose. For the same reasons, plus the likelehood that the virus arrived in NYC early and frequently, NYC's figures cannot be extrapolated to the rest of the state or country. I would like to see how these figures match up to the sewage-sampling method of estimation.
- deleted 6y ago[deleted]
- koheripbal 6y agoAs 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 a very biased sample. Very specifically, this bias excludes older people who are locking themselves away very very judiciously.
- mannykannot 6y agoThanks for your observations. If, however, behavior in NYC is more or less the same as elsewhere, then what might account for the difference in the results between store-customer sampling in the city and elsewhere? The results may well be biased from sampling shoppers, but if the bias is assumed to be from shopping behavior, and that behavior is essentially the same everywhere, why does it not wash out? One explanation might be that it got an earlier start in NYC, but both the hospitalizations and fatalities seem to have started showing up on about the same dates in the city and the surrounding suburbs. There seems to be a significant ethnic variation, but ethnicity is such a correlate to other issues that it is not likely to be informative on its own.
- wtvanhest 6y agoJust out of curiosity, what studies are you asking the OP to compare?
- wtvanhest 6y agoI’m a resident of SF downtown and previously DC and Boston. Everyone I know has stopped leaving their apartments/condos except for fresh air and are trying not to go to any stores. When possible are having food delivered. My friends in NYC have all left except for one who has a large apartment and no family without taking a flight. I think people see these studies of places they visited once and determine that those areas are way more dense and that they have seen the news and that all those deaths are due to tons of people having it. That is just not true. The studies are biased and likely this will go on for a long-time. We know this is way more deadly than the flu. That is obvious when you look at simple examples like the princess cruise in Japan. How often do 7+ people die on a cruise ship on a single voyage?