One of the things I teach in a unit on information retrieval is the notion of precision and recall, and tradeoffs between them, and the idea that a single "accu

One of the things I teach in a unit on information retrieval is the notion of precision and recall, and tradeoffs between them, and the idea that a single "accuracy" rate is almost never useful for these kinds of identification tasks. I've often thought that such a unit would be a good idea for journalists and people in general; the language of reporting on and talking about a lot of scientific advances (medical in particular) is so damn imprecise about this stuff. Even if they report only one number, they could at least say which one it is. 90% could plausibly be either the precision or the recall here, or even F-measure or some other average of them, but as you point out, it's unlikely to be "accuracy" in the sense of (true positives + true negatives) / N, or it wouldn't be very impressive.