A false positive test result is one that detects a marker when the disease is absent. A false negative test result is one that does not detect a marker when the disease is present. Operating characteristics of diagnostic tests and procedures are measures of the technical performance of these technologies. These characteristics are based on the probabilities of the four possible types of outcomes of a diagnostic test. The two most commonly used operating characteristics of diagnostic tests are sensitivity and specificity.
Sensitivity measures the ability of a test to detect disease when it is present.
Specificity measures the ability of a test to correctly exclude disease in a nondiseased person. Taken alone, sensitivity and specificity do not reveal the probability that a given patient really has a disease if the test is positive, or the probability that a given patient does not have the disease if the test is negative. These probabilities are captured by two other operating characteristics. Predictive value positive is the proportion of those patients with a positive test result who actually have the disease. Predictive value negative is the proportion of patients with a negative test result who actually do not have the disease.