Statistics Flashcards
What is the difference between sensitivity and specificity?
Sensitivity is the proportion of true positives (i.e., true patients) who are correctly identified as such.
Specificity is the proportion of true negatives (i.e., non-patients) who are correctly identified as such.
Specificity is profoundly affected by the population used to establish it—that is, the number and medical conditions in the control population. For example, the prevalence of rheumatoid factor in the general healthy population increases with age and is associated with a variety of non-rheumatic conditions (such as endocarditis and tuberculosis) and rheumatic diseases such as Sjögren’s syndrome and SLE. The calculated specificity in any given study will be increased by exclusion of the confounding conditions from the control group and decreased by the inclusion of older people or patients with SLE. Thus, specificity and sensitivity of a given test are greatly influenced by the pre-test probability that the condition is present in the test population.
