Negative predictive value

Negative predictive value (NPV) is a statistical measure used in medical testing and diagnostic medicine. It is defined as the proportion of patients with negative test results who are correctly diagnosed. It is a critical measure in assessing the performance of diagnostic tests.

Definition

The negative predictive value is defined as the probability that a person with a negative test result is truly disease-free. It is calculated using the formula:

NPV = TN / (TN + FN)

where TN is the number of true negatives and FN is the number of false negatives.

Importance

The NPV is an important measure in medical testing because it helps clinicians assess the accuracy of a test. A high NPV means that the test is reliable in ruling out the disease when the test result is negative. Conversely, a low NPV means that a negative test result is less reliable, and further testing may be needed to confirm the absence of disease.

Factors affecting NPV

The NPV of a test can be affected by several factors, including the prevalence of the disease in the population being tested and the sensitivity and specificity of the test. In general, the NPV increases as the prevalence of the disease decreases.

See also

• Positive predictive value
• Sensitivity and specificity
• Prevalence
• Diagnostic test

References

Negative predictive value Resources
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