U01.21.016 Sensitivity

Written by

Learning Objective:
Understand and apply the formula for Sensitivity, which measures the ability of a test to correctly identify those with the disease (true positives).

Formula:

$\text{Sensitivity} = \frac{TP}{TP + FN}$

Explanation:

TP (True Positives): Individuals who have the disease and test positive.
FN (False Negatives): Individuals who have the disease but test negative.
Sensitivity reflects how good a test is at detecting disease when it is truly present.

Interpretation:

High sensitivity → few false negatives → good for screening tests (rule out disease).
Use the mnemonic “SnNout” — a highly SeNsitive test, when Negative, rules out disease.

Example:

If a test correctly identifies 90 out of 100 diseased patients:
$TP = 90$ , $FN = 10$