Learning Objective:
Understand and apply the formula for NPV, which measures the probability that a patient with a negative test result truly does not have the disease.

Formula:

Explanation:

• TN (True Negatives): Patients who do not have the disease and test negative.
• FN (False Negatives): Patients who have the disease but test negative.
• NPV indicates how likely a negative test result truly reflects the absence of disease.

Interpretation:

• High NPV → most negative results are true negatives
• Influenced by disease prevalence: lower prevalence → higher NPV

Example:

If a test identifies 80 true negatives and 20 false negatives:
,

✅ Answer: NPV = 80%