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Sensitivity (also called the true positive rate, or the recall in some fields) measures the proportion of positives that are correctly identified as such (e.g., the percentage of sick people who are correctly identified as having the condition).
Specificity (also called the true negative rate) measures the proportion of negatives that are correctly identified as such (e.g., the percentage of healthy people who are correctly identified as not having the condition).
A worked exampleA diagnostic test with sensitivity 67% and specificity 91% is applied to 2030 people to look for a disorder with a population prevalence of 1.48% | Patients with bowel cancer
(as confirmed on endoscopy) | Condition positive | Condition negative | Fecal
occult
blood
screen
test
outcome | Test
outcome
positive | True positive
(TP) = 20 | False positive
(FP) = 180 | Positive predictive value = TP / (TP + FP)
= 20 / (20 + 180)
= 10% | Test
outcome
negative | False negative
(FN) = 10 | True negative
(TN) = 1820 | Negative predictive value = TN / (FN + TN)
= 1820 / (10 + 1820)
≈ 99.5% | | Sensitivity = TP / (TP + FN)
= 20 / (20 + 10)
≈ 67% | Specificity = TN / (FP + TN)
= 1820 / (180 + 1820)
= 91% |
Related calculations |
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