Sensitivity is defined as the proportion of what?

• A. True Positives divided by (True Positives plus False Negatives).
• B. True Negatives divided by (False Positives plus True Negatives).
• C. False Positives divided by (False Positives plus True Negatives).
• D. False Negatives divided by (True Positives plus False Negatives).

Answer: (A)

Sensitivity is the test’s ability to correctly identify those who actually have the disease. It is the proportion of actual positives that the test labels as positive, calculated as true positives divided by (true positives plus false negatives). This denominator includes everyone who truly has the disease, so sensitivity reflects how well the test detects disease rather than misses it. The other formulas describe different ideas: specificity (true negatives over all non-diseased), the false positive rate (false positives among non-diseased), and the false negative rate (false negatives among those with disease).