In a test, sensitivity and specificity are two criteria that help determine whether a person is suffering from a certain disease or not, and a specificity of 100% means that all healthy people (without the disease) are identified as healthy.

In medicine, sensitivity analysis can describe how well a test detects a particular disease or condition in people who actually have it. Sensitivity can also refer to how the body reacts to the environment or to drugs, chemicals, or other substances.