Anything with 20% false negatives is fine if you expect to have five or more hireable people apply every time you advertise. But if you are in a situation where you might get 200 people applying and perhaps one or sometimes two are actually worth hiring, a 20% false negative is crippling.
This point does not get addressed nearly enough. Aline (I think?) mentioned elsewhere in the thread that much of the conventional wisdom on hiring has come from Google and other companies with deep hiring pipelines. Google can afford high false positive rates because their pipeline still generates sufficient numbers of hires in spite of it. This fact seems to be lost on most of the small companies trying to cargo-cult their hiring practices.
