Positive Predictive Value Calculator | PPV Calculator

Calculator

True positives (TP)

True Positives (TP) = patients who have the disease AND tested positive. These are the correct positive results. In SPSS Crosstabs: Disease=Yes row, Test=Positive column. Example: 45 diseased patients with a positive test.

False positives (FP)

False Positives (FP) = patients who do NOT have the disease BUT tested positive (false alarm). In SPSS Crosstabs: Disease=No row, Test=Positive column. Example: 20 healthy patients incorrectly tested positive. PPV = TP ÷ (TP + FP) = 45 ÷ 65 = 69.2%. PPV drops in low-prevalence populations even if sensitivity and specificity stay the same.

Required Terms Explained

Positive predictive value = TP / (TP + FP). It answers: if the test is positive, what is the probability the patient truly has the disease?

TP: correct positive test result.

FP: false positive result.

PPV depends on prevalence: PPV changes when disease prevalence changes, even if sensitivity and specificity stay the same.