By failing to give the false-negative probability, you make the exact answer incalculable.

ECONOMIST: Letters | The

The probability of a false positive in a chemical assay for a drug or poison (something appearing to show up when it isn't really there) is reasonably well known.

ECONOMIST: Whose body of evidence? | The

If one in 1, 000 people have a disease and the false-positive rate for a test is 5%, then the probability that a person testing positive has the disease is at most 2%.

ECONOMIST: Letters | The