TATITIC CALCULATOR
False Positive Paradox
A precise tool.
What is the False Positive Paradox & How does it work?
The false positive paradox occurs when a medical test with high sensitivity and specificity still produces more false‑positive results than true‑positive results because the condition being screened for is extremely rare.
Key parameters are sensitivity (the probability the test is positive given disease), specificity (the probability the test is negative given no disease), and prevalence (the proportion of the population that actually has the disease).
PPV = \frac{Se \times P}{Se \times P + (1 – Sp) \times (1 – P)}
PPV = Positive Predictive Value
When prevalence is low, the denominator is dominated by the false‑positive term, driving the PPV down and illustrating why screening large populations for rare diseases can be misleading.
Parameters
Result
—
Frequently Asked Questions
What is false positive paradox?
False positive paradox occurs when a rare disease has a high number of false positives despite a test having high sensitivity and specificity.
How does prevalence affect the false positive paradox?
Low prevalence increases the likelihood of false positives because the absolute number of people without the disease is much higher than those with it.
What is PPV in this calculator?
PPV stands for Positive Predictive Value, which is the probability that a positive test result truly indicates the presence of the disease.
Can you explain sensitivity and specificity?
Sensitivity is the test’s ability to correctly identify those with the disease. Specificity is the test’s ability to correctly identify those without the disease.
When would I use this calculator?
Use this calculator when evaluating a medical test’s reliability, especially in conditions where the disease prevalence is low.
What does a high PPV indicate?
A high PPV indicates that a positive test result is more likely to be true, reducing the likelihood of false positives.
How do I interpret the results from this calculator?
The results show the PPV, helping you understand how reliable a positive test result is in the context of the disease’s prevalence.
Results are for informational purposes only and do not constitute professional advice.