For example, say you get tested five times in a week, and all five of your tests come back negative. Your coworker also got tested five times, but one of his tests came back positive. Of the 10 tests taken, 10% came back positive; that’s how the state gets its positivity rate. But of the two of you, 50% got at least one positive result, and that’s how Hopkins' positivity rate is determined. Same situation, different use of data; same term, different result.