PPV and NPV at a chosen prevalence
The 2×2 calculator uses the prevalence inside your table. This one moves the same sensitivity and specificity into the population you actually screen.
Per 1,000 people at this prevalence
Questions
Why is PPV lower than sensitivity?
Sensitivity is the share of people with the condition that the test finds. Positive predictive value is the share of positive tests that are truly positive. When the condition is rare, most positives are false positives, so PPV falls even if sensitivity stays high.
Which prevalence should I enter?
Use the prevalence in the population you will actually test. Do not reuse the prevalence from a case-control study, where cases were enrolled on purpose.
How is this different from the diagnostic 2×2 calculator?
The 2×2 calculator uses the prevalence implied by your true-positive, false-positive, false-negative, and true-negative counts. This page keeps sensitivity and specificity fixed and lets you change prevalence.
Educational only. Not medical advice, not a regulatory determination, and not a substitute for qualified RA/QA, legal, clinical, or statistical counsel. Prevalence-adjusted PPV does not submit to FDA, Notified Bodies, or IRBs.