The quality of a screening test is described in terms of its accuracy in telling who truly has a disease (its sensitivity) and who truly does not (its specificity). The goal of any screening test is to identify correctly those people who have a certain disease (100 percent sensitivity). An ideal screening test would also be able to identify correctly all the people who do not have the disease (100 percent specificity). A perfect test would be able to identify everyone accurately with no mistakes. There would be no false negatives (when people who have the disease are missed by the test) and no false positives (when healthy people are incorrectly shown to have the disease).
However, there is no perfect screening test with 100 percent sensitivity and 100 percent specificity. There is always a trade-off between the two. A test that is very sensitive will pick up even the slightest abnormality. This means that it will miss few cases of disease, but it may also misidentify healthy people as having the disease when they actually don't. This can lead to further testing and some anxious moments for what turns out to be a benign diagnosis. A test that is very specific, on the other hand, will have fewer false positive results, but may miss more cases of disease. This balance between sensitivity and specificity is important for all screening tests, including mammography and clinical breast exam.
Learn more about the accuracy of mammography.
Learn more about the accuracy of clinical breast exam.
Updated 10/02/09
