Calculating Test Sensitivity and Specificity
Gold Standard | ||||
Disease Present | Disease Absent | Total | ||
Test Result | Positive | a | b | a + b |
Negative | c | d | c + d | |
Total | a + c | b + d | ||
a = True positives; the test has correctly diagnosed the disease b = False positives; the test is positive but disease is absent c = False negatives; the test is negative but disease is present d = true negatives; the test correctly diagnosed the absence of disease Sensitivity is the true positives divided by the sum of the true positives and the false negatives: a/(a + c) Specificity is the true negatives divided by the sum of the true negatives and the false positives: d/(b + d) | ||||