Using data from a 2×2 table, sensitivity is calculated as:

Correct answer: A. TP / (TP + FN)

• A. Correct. Sensitivity = TP / (TP + FN). It measures the proportion of truly positive cases correctly identified by the test — the test's ability to detect disease when disease is present ('detect the sick').
• B. TN / (TN + FP) = Specificity — the ability to correctly identify those WITHOUT the disease.
• C. TN / (TN + FN) = Negative Predictive Value (NPV) — the probability that a negative test truly doesn't have the disease.
• D. TP / (TP + FP) = Positive Predictive Value (PPV) — the probability that a positive test actually has the disease.