Illustration of problem of False positives
and False negatives when testing for HIV antibody.
TEST
| Positive | Negative | Totals | ||
| Disease | Present | Sensitivity | False - | |
| Not Present | False+ | Specificity |
TEST
| Positive | Negative | Totals | ||
| Disease | Present | 196 | 4 | 200 |
| Not Present | 19996 | 979804 | 999800 | |
| Totals | 20192 | 979808 | 1,000,000 |
Prevalence = 2/1000, Sensitivity = 0.98, Specificity = 0.98
What can you deduce about the ability to provide useful information by mass testing a population for a rare disease e.g. all poeple applying for a marriage license for HIV?