Illustration of predictive value of a positive test (PVP) in high and low prevalence populations
| Prevalence of chlamydia in population | 10% (high) | 2% (low) | |
| True positives among 1000 women | 100 | 20 | |
| True positives detected by the test (sensitivity = 92.6%) | 92 | 18 | |
| False positives given by the test (specificity = 99.4 (0.6 false positives per 100) | 6 | 6 | |
| Predictive value positive (PVP) = true positives/total positive results | 92/98 (94%) | 18/24 (75%) |