There is a reason why they have 3% and it has nothing to do with science. It’s the threshold that was negotiated with the teachers union in NYC. That’s why you have other regions in NY with schools still open even though they have higher than 3%The 3% positivity rate threshold for NYC school closure does seem low to me, but I do not know what the science is behind that rate and I assume that there is some reason they went with that rate.