Sensitivity and Specificity

Sensitivity and specificity:
Ideally every test would be 100% sensitive and specific. The best way to illustrate sensitivity and specificity in terms of a pregnancy test. A pregnancy test that is very sensitive will not miss any women who are pregnant, however, it may give false positives to women who actually aren’t pregnant and potentially scare a lot of dudes! This test would be highly sensitive and not so specific.

A test that has high specificity will not have false positives but may also have some false negatives meaning women who are actually pregnant would have a negative result. This test would be highly specific but not so sensitive.

There are formulas that can be used to calculate sensitivity and specificity.

Sensitivity is calculated using the following equation: (TP / (TP + FN))
TP = true positive, FN = false negative

Specificity is calculated using the following equation: (TN / (TN+ FP))
TN = true negative, FP = false positive

Study Tip
Use the phrase “sense the TP” (like what you do in the middle of the night in the bathroom) to remember these formulas. If you can remember the equation for sensitivity, the formula for specificity can be had by swapping P for N and N for P.