> From there, they scale up to the state level and claim 12% incidence statewide. The news story says it is using the same calculation, but it can't be—how did they get from 6.6% to 12%?

You have more data from LA: https://reason.com/2020/04/20/l-a-county-antibody-tests-sugg... 12% and more I believe is from NYC: https://www.livescience.com/covid-antibody-test-results-new-...