Sensitivity

Sensitivity is the proportion of truly positive people (by the reference standard) whom the test flags as positive: true positives divided by all positives. A test with high sensitivity misses few affected people; a negative result then makes the condition less likely (how much less also depends on prevalence).

Example: Of 50 children with a diagnosis, 45 are flagged by the screening: sensitivity = 90% (95% CI 79 to 96%).

Caution: Sensitivity and specificity move in opposite directions when the cut-off of the test is changed. With few affected people the interval is wide.