>>14114263It's a simple base-rate question, and because I called it simple, watch me fuck it up.
Let's say 100 tests performed on a representative sample, so 10 people with hep C and 90 people without hep C.
Of the 10 people with hep C, we expect 9 positive results and 1 negative result.
Of the 90 without hep C, we expect 36 positive results and 54 negative results.
So we have 9 + 36 = 45 positive results, 9 of which are correct, or 20%.
Doctors can give the patient hep C to increase the certainty.
