What factor does negative predictive value depend on?

Negative predictive value (NPV) is the probability that individuals with a negative test result truly do not have the disease. This probability is highly influenced by the prevalence of the disease in the population being tested.

When the prevalence of a disease is high, even tests with decent specificity can yield a lower NPV because there are more true positive cases. Conversely, in a population where the disease prevalence is low, even tests that might not be very sensitive can have a high NPV, as the majority of negative results will correspond to individuals who truly do not have the disease.

In summary, NPV is affected by how common the disease is in the population; if fewer people have the disease, the likelihood that a negative test result corresponds to a true negative increases, resulting in a higher NPV.