Measures of Diagnostic Accuracy: Sensitivity, Specificity, PPV and NPV

INtroDuctIoN In biomedical studies, diagnostic tests are used to determine the presence or absence of diseases in study subjects. Examples include testing for the presence or absence of Alzheimer’s disease and invasive carcinoma. A diagnostic test is validated by comparing test results against a gold standard that establishes the true status of the subject. Test validation is an evaluation method used to determine the fitness of a test for a particular use and through it, one can assess how good the test is at identifying subjects with and without a disease or condition. Validation involves calculating four objective measures of test performance, namely, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). The ideal diagnostic test would correctly identify subjects with and without the disease with 100% accuracy. Details of the four measures are provided below.