Part III Intercollegiate exam / Email to friend


See Wkipedia for a worked example http://en.wikipedia.org/wiki/Sensitivity_%28tests%29

Relationships among terms

Condition
(as determined by "Gold standard")

True False

Test
outcome Positive True Positive False Positive
(Type I error, P-value) → Positive predictive value

Negative False Negative
(Type II error) True Negative → Negative predictive value

↓
Sensitivity ↓
Specificity

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

Patients with bowel cancer
(as confirmed on endoscopy)

True False ?

FOB
test Positive TP = 2 FP = 18 = TP / (TP + FP)
= 2 / (2 + 18)
= 2 / 20 ≡ 10%

Negative FN = 1 TN = 182 = TN / (TN + FN)
182 / (1 + 182)
= 182 / 183 ≡ 99.5%

↓
= TP / (TP + FN)
= 2 / (2 + 1)
= 2 / 3 ≡ 66.67% ↓
= TN / (FP + TN)
= 182 / (18 + 182)
= 182 / 200 ≡ 91%

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Sensitivity and Specificity