How to use the positive and negative predictive value calculator
Find the chance a positive or negative test result is correct, given sensitivity, specificity and disease prevalence. Enter sensitivity, specificity, prevalence in population in the fields above; the positive predictive value, negative predictive value are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “positive predictive value”, “negative predictive value”, “how accurate is a positive test”, “calculate positive and negative predictive value”, “find positive predictive value”.
Formula
Variables
- sens — Sensitivity
- spec — Specificity
- prev — Prevalence in population
Worked example
With sensitivity = 0.9, specificity = 0.95, prevalence in population = 0.01, the calculator gives positive predictive value ≈ 15.38462 %; negative predictive value ≈ 99.89379 %.
Frequently asked questions
What is the positive and negative predictive value calculator used for?
Find the chance a positive or negative test result is correct, given sensitivity, specificity and disease prevalence. It helps with questions such as “positive predictive value”, “negative predictive value”, “how accurate is a positive test”.
What is the formula for the positive and negative predictive value calculation?
Positive predictive value (%) = 100 × sens × prev / (sens × prev+(1-spec) × (1-prev)). Negative predictive value (%) = 100 × spec × (1-prev) / (spec × (1-prev)+(1-sens) × prev). Here sens is sensitivity, spec is specificity, prev is prevalence in population.
What inputs do I need for the positive and negative predictive value calculator?
You need sensitivity, specificity, prevalence in population. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the positive and negative predictive value calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the positive and negative predictive value result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.