There can be false negatives, but at this positive level false positives are less of an issue than at low levels. Also, they apparently specifically grabbed people out and about at grocery stores, so very sick people may have been excluded, pushing levels down. On the other hand, people shopping might be more likely to pick it up.
EDIT: Apparently this test also only detect IgG, which is the type of antibody that rises last and can take two weeks or more to be detectable in some people after symptoms develop.
UPDATE as of 4/23/2020.
I’m so sick of being right.
Seroprevalence in NYC reported as 21%.
https://twitter.com/NYGovCuomo/status/1253353516803993600
There can be false negatives, but at this positive level false positives are less of an issue than at low levels. Also, they apparently specifically grabbed people out and about at grocery stores, so very sick people may have been excluded, pushing levels down. On the other hand, people shopping might be more likely to pick it up.
Pretty much right on the nose...
https://twitter.com/trvrb/status/1253398329766973441
″ If we then take deaths as of today as 17,200 based on excess deaths (https://nytimes.com/interactive/2020/04/21/world/coronavirus-missing-deaths.html), we’d get an infection-to-fatality ratio of ~1%. ” I suspect the true seropositivity is higher than the measured due to selection effects on the net, which would push this down a bit.
EDIT: Apparently this test also only detect IgG, which is the type of antibody that rises last and can take two weeks or more to be detectable in some people after symptoms develop.