Which formula represents negative predictive value (NPV)?

Negative Predictive Value (NPV) measures the likelihood that a patient who tests negative actually does not have the disease. It helps to interpret the effectiveness of a diagnostic test in identifying patients without the condition.

The formula for NPV is defined as the number of true negatives (TN) divided by the total number of negative test results, which includes both true negatives (TN) and false negatives (FN). This relationship is mathematically expressed as:

NPV = TN / (TN + FN)

In this context, a true negative represents a correct identification of a non-disease case, while a false negative indicates a disease case that was incorrectly identified as negative. Thus, understanding NPV is crucial for evaluating the reliability of a test for ruling out disease.

This formula emphasizes the importance of both accurate identification of non-diseased individuals and the capacity to recognize missed cases of the disease when interpreting a test's negative result.