This is a measure of accuracy for screening tests that refers to true positives — the probability that subjects with a positive result test truly do have the disease or condition. So if a person is tested and receives a positive result, how likely is it that the result is correct? How worried do they need to be? Knowing the positive predictive value (PPV) can determine how many false positives are occurring with a test.
Deeper dive
Positive predictive value is derived from the same numbers needed to quantify the sensitivity and specificity of a test, but PPV also depends on the population being tested and the prevalence of the disease in that population. For example, if you were screening only non-smoking women of a healthy weight in their 20s for breast cancer, the PPV is likely to be very low, with a high rate of false positives, because prevalence of breast cancer is very low in this population. On the other hand, if you were doing breast cancer screenings exclusively in women in their 70s who carry a BRCA mutation for breast cancer, the PPV is likely to be very high, with a low rate of false positives, because breast cancer is far more prevalent in this population.