PPV and NPV Dibaba

Negative Predictive Value (NPV)

• Definition: The Negative Predictive Value is the probability that subjects who have tested negative for a disease actually do not have the disease.

• Formula: $NPV = \frac{TN}{TN + FN}$ where:

  • TN is True Negatives

  • FN is False Negatives

• Interpretation: A high NPV indicates that a negative test result is a good indicator that the individual does not have the disease.

Positive Predictive Value (PPV)

• Definition: Positive Predictive Value is the probability that subjects who have tested positive for a disease actually have the disease.

• Formula: $PPV = \frac{TP}{TP + FP}$ where:

  • TP is True Positives

  • FP is False Positives

• Interpretation: A high PPV indicates that a positive test result is a good indicator that the individual has the disease.

Comparison of Screening and Confirmatory Tests

• Screening Test: A test designed to identify individuals who may have a disease.

  • Example: This can be visually and clinically assessed before more invasive testing (e.g., necropsy).

• Confirmatory Test (Necropsy): A definitive test used to confirm whether or not an individual has the disease.

  • Advantages: Provides a more accurate assessment than screening tests.

Justification for Test Results

• Clinical Observations: The statement references observing signs (like edema) but acknowledges uncertainty in the exact figures used for diagnosis (e.g., 76 or 764).

• Importance of Accuracy: The validity of a test result can influence decisions and required actions based on the probability of having the disease.

Summary

• The Negative Predictive Value is crucial in understanding how reliable a test is when its outcome is negative, while Positive Predictive Value assesses reliability when the outcome is positive.

• The distinction between screening tests and confirmatory tests is essential in clinical diagnostics.