Non-clinical sciences/Stats & evidence · Test characteristics

Specificity

What it means

TN / (TN + FP) — probability a test is negative in those WITHOUT the disease. A highly specific test, when positive, rules disease IN (SpPIN). Used to confirm after a sensitive screen.

Worked example

HIV pathway: sensitive ELISA screen → highly specific confirmatory assay before diagnosis.

In the exam

A test rarely falsely flags healthy people, so a positive result confirms the disease — it is used after a screening test.

What settles it

Specificity = SpPIN (rule-in/confirm); sensitivity = SnNOUT (rule-out/screen). Neither depends on prevalence.

Classically confused with

Sensitivity

Source: StatPearls — Sensitivity and Specificity