specificity is an important criteria for screening and diagnostic instruments, the specificity of a test reflects the probability that the screening test will be negative among those who, in fact, do not have a disease.
A test that is 90% specific will identify 90% of patients who do not have the disease. Tests with a high specificity (a high true negative rate) are most useful when the result is positive. A highly specific test can be useful for ruling in patients who have a certain disease.
