Originally posted as a Twitter thread on November 18, 2020

The absurdity of closing ALL SCHOOLS based on the positivity rate of a (presumably selection-biased sick?) less than 1% sample of the population should offend anyone who understands what a fraction is

NYC had 66K tests out of an 8M population. If you only test sick people, you will get a high positivity rate! If you over-test healthy people, you could make Ebola seem pleasant based on its “low positivity rate”
Positivity rate is garbage