Sensitivity and Specificity

Sensitivity and Specificity

Sensitivity is the ability to correctly identify those who have the disease.

Specificity is the ability to correctly identify those who do not have the disease.

Ideally, a test should have 100% sensitivity and 100% specificity. In other words, the test always correctly identifies the disease state of the people tested.

Result of Screening	Disease State
Result of Screening	Disease	No Disease
Positive	true positive	false postive
Negative	false negative	true negative

The people who have the disease are the "true positives." The people who do not have the disease are the "true negatives."

Sensitivity = ( "true positives" divided by ("true positives" + "false negatives") ) multiplied by 100 (to make it a percentage)

When the "false negatives" is a small number relative to the "true positives", sensitivity approaches 100%.

Specificity = ( "true negatives" divided by ("true negatives" + "false positives") ) multiplied by 100 (to make it a percentage)

When the "false positives" is a small number relative to the "true negatives", specificity approaches 100%.