Practical Application in Screening
Mar 28, 2025
Scenario: Consider a screening test for a disease in a population of 1,000 individuals. The prevalence of the disease is 10%.
- True Positives (TP): 90
- False Positives (FP): 20
- True Negatives (TN): 880
- False Negatives (FN): 10
Sensitivity:
- Calculation: Sensitivity = TP / (TP + FN) = 90 / (90 + 10) = 90%
- Interpretation: The test correctly identifies 90% of those with the disease.
Specificity:
- Calculation: Specificity = TN / (TN + FP) = 880 / (880 + 20) = 97.8%
- Interpretation: The test correctly identifies 97.8% of those without the disease.
Positive Predictive Value (PPV):
- Calculation: PPV = TP / (TP + FP) = 90 / (90 + 20) = 81.8%
- Interpretation: 81.8% of individuals with a positive test result actually have the disease.
Negative Predictive Value (NPV):
- Calculation: NPV = TN / (TN + FN) = 880 / (880 + 10) = 98.9%
- Interpretation: 98.9% of individuals with a negative test result do not have the disease.
