That's because the methods and authors have major overlap. The USC study reported here is a collaboration with the same group at Stanford: https://news.usc.ed

That's because the methods and authors have major overlap. The USC study reported here is a collaboration with the same group at Stanford: https://news.usc.edu/168810/usc-covid-19-antibody-researcher-answers-questions-about-testing-in-l-a-county/ https://news.usc.edu/168810/usc-covid-19-antibody-researcher... The participant selection here was done differently, but the same problems arise with the false positive rate of the tests.