E-Epidemiology
Sensitivity
Remember that such an imperfect test can provide false negative results, i.e. a negative test from sick animals.
This is described by the diagnostic test sensitivity = probability of having a positive test result among sick animals:
| Sensitivity (SE) = probability P (Test+ | Disease+) |
In our contingency table this would be: a / (a + c), with cell a showing the number of true positive animals and the sum of cells a and c referring to all sick animals.
Thus, the test sensitivity represents the correct positive fraction of test results.
| Disease + |
Disease - | Total | |
| Test + |
a |
b |
a + b |
| Test - | c |
d |
c + d |
| Total | a + c |
b + d | a + b + c + d |