Now comes our first batch of definitions.
- True positive (TP): Positive test result matches reality — the person is actually sick and tested positive.
- False positive (FP): Positive test result doesn’t match reality — the test is positive but the person is not actually sick.
- True negative (TN): Negative test result matches reality — the person is not sick and tested negative.
- False negative (FN): Negative test result doesn’t match reality — the test is negative but the person is actually sick.
Folks get confused with these often, so here’s a useful heuristic: positive vs. negative reflects the test outcome; true vs. false reflects whether the test got it right or got it wrong.
It’s a nice read. The next step, after understanding these, is figuring out in which circumstances we want to weigh some of these measures more than others.