Template:SensSpecPPVNPV


 * Relationships among terms:


 * A worked example: the Fecal occult blood (FOB) screen test is used in 203 people to look for bowel cancer:

Related calculations
 * False positive rate (α) = FP / (FP + TN) = 18 / (18 + 182) = 9% = 1 - specificity
 * False negative rate (β) = FN / (TP + FN) = 1 / (2 + 1) = 33% = 1 - sensitivity
 * Power = 1 − β

Hence with large numbers of false positives and few false negatives, a positive FOB screen test is in itself poor at confirming cancer (PPV=10%) and further investigations must be undertaken, it will though pickup 66.7% of all cancers (the sensitivity). However as a screening test, a negative result is very good at reassuring that a patient does not have cancer (NPV=99.5%) and at this initial screen correctly identifies 91% of those who do not have cancer (the specificity).