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False Positive Base-Rate Calculator — result sheet
Calculate positive predictive value and negative predictive value from prevalence, sensitivity, and false-positive rate.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: PPV=(sensitivity×prevalence)/(sensitivity×prevalence+false-positive rate×(1−prevalence)); NPV=(specificity×(1−prevalence))/(specificity×(1−prevalence)+(1−sensitivity)×prevalence).
The same test characteristics can produce different predictive values when the base rate changes; the page makes that base-rate calculation explicit.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Prevalence — %; minimum 0; maximum 100
- Sensitivity — %; minimum 0; maximum 100
- False-positive rate — %; minimum 0; maximum 100
Worked example
| Input | Value |
|---|---|
| Prevalence | 1 |
| Sensitivity | 90 |
| False-positive rate | 5 |
PPV ≈ 15.38%; NPV ≈ 99.90%.
Assumptions and limits
- The entered rates describe the same population and threshold.
- False-positive rate is one minus specificity.
- This is a probability illustration, not medical advice, diagnostic validation, or a treatment decision.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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