What is Screening
The presumptive identification of an unrecognized disease or defect by the application of tests, examinations or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not. A screening test is not intended to be diagnostic. Persons with positive or suspicious findings must be referred to their physicians for diagnosis and necessary treatment
Understanding Sensitivity, Specificity, PPV, and NPV
Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) are essential measures used in diagnostic testing to assess the accuracy of a test in identifying true positives, true negatives, false positives, and false negatives.
- Sensitivity: Refers to the ability of a test to correctly identify individuals with the disease (true positive rate).
- Specificity: Refers to the ability of a test to correctly identify individuals without the disease (true negative rate).
- PPV: Refers to the probability that an individual with a positive test result actually has the disease.
- NPV: Refers to the probability that an individual with a negative test result does not have the disease.
Example Calculations
| Test Result | COVID Present | COVID Present |
|---|---|---|
| Positive | 90 (True Positive) | 80 (False Positive) |
| Negative | 20 (True Positive) | 160 False Positive) |
Example Calculations
- Sensitivity = TP / (TP + FN) = 90 / (90 + 20) = 81.8%
- Specificity = TN / (TN + FP) = 160 / (160 + 30) = 84.2%
- PPV = TP / (TP + FP) = 90 / (90 + 30) = 75%
- NPV = TN / (TN + FN) = 160 / (160 + 20) = 88.9%
Interpretations
- Sensitivity: The test has a sensitivity of 81.8%, indicating a good ability to detect the disease.
- Specificity: The specificity of 84.2% is similar to the previous example, suggesting a good ability to minimize false positives.
- PPV: The PPV of 75% means that there is a 75% chance that an individual with a positive test result actually has the disease. This suggests a moderate positive predictive power.
- NPV: The NPV of 88.9% indicates a strong probability that an individual with a negative test result does not have the disease.