[ptrincr]

Apologies for the way this was linked to. The 6% is from this study:

https://www.miamidade.gov/releases/2020-04-24-sample-testing...

"Our data from this week and last tell a very similar story. In both weeks, 6% of participants tested positive for COVID-19 antibodies, which equates to 165,000 Miami-Dade County residents"

That is what the commentator is referring to in the linked post.

So if you plug their own figures into the calculator:

Sensitivity .8866 Specificity .9063

and a Prevalence of .06 based on the study, you get the 62% false positive rate.

As the prevalence increases, as with the NYC study which found the positive rate to be 21% (prevalence), the false positive rate decreases, down to 28% of the NYC study.