False Positive Calculator

What Are False Positives?

A false positive occurs when a healthy person receives a positive diagnostic test result. This calculator estimates false positives, true negatives, and the false positive rate from disease prevalence and test specificity. For full confusion matrix metrics, see the Accuracy Calculator.

Key Formulas

$$\text{False positives} = (1 - \text{Specificity}) \times (1 - \text{Prevalence})$$

$$\text{True negatives} = \text{Specificity} \times (1 - \text{Prevalence})$$

$$\text{False positive rate} = 1 - \text{Specificity}$$

Example

With 5% disease prevalence and 93% test specificity, the false positive rate is 7%. Among a population of 10,000, about 665 healthy people would test positive incorrectly.

Related Tools

• False Positive Paradox Calculator
• Bayes Theorem Calculator
• Accuracy Calculator