E-Epidemiology
To remember
In the general case:
| Disease + |
Disease - | Total | |
| Test + |
a |
b |
a + b |
| Test - | c |
d |
c + d |
| Total | a + c |
b + d |
a + b + c + d |
Remember:
Positive predictive value: Proportion of test – positive individuals that actually are sick
PPV = P (Disease + | Test positive) = a / (a + b)
Negative predictive value: Proportion of test – negative individuals that actually are healthy
NPV = P (Disease- | Test negative) = d / (c + d)