Diagnostic tests (1) – sensitivity and specificity

An important area of medical research concerns the use of tests to diagnose individuals with conditions. The simplest situation occurs when we use a diagnostic test to determine whether an individual has a particular condition or not; and thus we have a ‘yes’ or ‘no’ answer. We need a method to be able to assess whether a new diagnostic test is accurate, and therefore likely to be useful in clinical practice. The accuracy of a diagnostic test is usually assessed by calculating the test’s sensitivity and specificity. Here, we investigate these two concepts. We will do so with the help of a hypothetical example, described below.