Sensitivity & Specificity
Direct answer: Sensitivity is the true-positive rate; specificity is the true-negative rate. In practice PPV and NPV matter more, because they account for how common the condition is.
The two core measures of diagnostic accuracy — and two more you actually care about in practice.
| Measure | Meaning | What it answers |
|---|---|---|
| Sensitivity | True positive rate | How well does it catch people who DO have the condition? |
| Specificity | True negative rate | How well does it avoid false positives in people who DON'T? |
| PPV | Positive predictive value | If it's positive, how likely is it a true positive? (depends on prevalence) |
| NPV | Negative predictive value | If it's negative, how likely is it a true negative? |
Why PPV/NPV matter
A test with 95% sensitivity and 95% specificity can still give mostly false positives in a low-prevalence population — that's why confirmatory testing and prevalence context matter.
See also rapid test vs PCR and IgG vs IgM.
By Progene Bio Regulatory Affairs Team · Medical Device QA · Medical disclaimer · Last reviewed: 2026-09-12