E-Epidemiology
Negative predictive value
Given a negative test result what is the probability that the individual is truly healthy?
This is evaluated by the test negative predictive value:
| Negative predictive value NPV = probability P (Disease - | Test -) |
In our contingency table this would be: d / (c+d), with cell d showing the number of true negative animals and the sum of cells c and d referring to all negative animals.
Thus, the negative predictive value represents the proportion of individuals who test negative who are actually healthy.
| Disease + |
Disease - | Total | |
| Test + |
a |
b |
a + b |
| Test - | c |
d |
c + d |
| Total | a + c |
b + d | a + b + c + d |