1/ This has been bothering me for a while: Are repeated COVID tests for past infection independent? More precisely, if I take a test and it is negative and I take the same test again and it is negative, how confident I am that I did not previously have COVID?
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2/ This is prompted, obviously, by me being an entirely typical human being who had an uncharacteristically bad case of viral pneumonia in February that I got from my parents, who had negative flu tests for the same cold three weeks before that.
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3/ Recently, I had two tests, both of which came back negative. Being a sloppy Bayesian, I used the second to update my updated prior, and concluded, "okay, I probably did not have it."
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4/ But, combined with the curious evidence that additional family members got much more sick with negative results — so much so that they were looking for an environmental containment in their home — the slightly-less-sloppy bayesian revisited the testing assumption.
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5/ I don't know much about immunology. But the idea of independent errors for repeated tests on a condition we're still learning about seems to assume *a lot* of homogeneity in responses and strains that make me a little skeptical. So I'd like someone to explain it / correct me.
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from what i understand, if your immune system beat it off, most tests (in particular PCR) will come back negative (reasoning is that negative tests are used to confirm if you have recovered).
i think antibody tests might not.
a lot depends on what the test is. cc @DrEricDing
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