Effect of disease prevalence on predictive values

This figure illustrates how the positive and negative predictive value of a diagnostic test vary depending on the prevalence of the disease.

Consider a population of 2000 people who undergo testing with a diagnostic test that has a sensitivity and specificity of 90%:

Panel A (high prevalence): The 2x2 table in panel A shows the predictive values when the disease prevalence is high (50%). In this scenario, the positive and negative predictive values will be similar to the sensitivity and specificity (90%, respectively).
Panel B (low prevalence): By contrast, the 2x2 table in panel B shows the predictive values when the disease prevalence is low (10%). In this scenario, the positive predictive value is substantially lower (50%), though the negative predictive value is higher (99%).

Graphic 68072 Version 4.0