Sensitivity - describes how accurately a test can classify impaired individuals as impaired. For example, a test with 97% sensitivity correctly classifies 97 out of 100 impaired individuals as "Impaired" and incorrectly classifies 3 out of 100 impaired individuals as "Normal".

Specificity - describes how accurately a test classifies normal individuals as normal. For example, a test with 80% specificity, correctly classifies 80 out of 100 normal individuals as "Normal" and 20 out of 100 normal individuals as "Impaired".

Importantly, when evaluating a particular test's sensitivity, specificity and overall accuracy, it is essential to understand the stage of impairment detected by the test. For example, the Mini-Mental State Exam (MMSE) is a widely-used tool for tracking dementia but is not accurate for detecting earlier stages of memory loss.