Table 2
Definition of common measures of test accuracy
| Test accuracy measure | Formula* | Definition |
|---|---|---|
| Sensitivity | a/(a+c) | Proportion of those with the target condition correctly identified as having the condition |
| Specificity | d/(b+d) | Proportion of those without the target condition correctly identified as not having the condition |
| Positive predictive value | a/(a+b) | Proportion of those with the target condition out of the test positives |
| Negative predictive value | d/(c+d) | Proportion of those without the target condition out of the test negatives |
| Positive likelihood ratio (LR+) |  | Ratio of the proportion that tests positive among those with the target condition compared to the proportion that tests positive among those without the target condition |
| Negative likelihood ratio (LR–) |  | Ratio of the proportion that tests negative among those with the target condition compared to the proportion that tests negative among those without the target condition |
| Diagnostic OR | ad/bc or LR+/LR– | Ratio of the odds of positivity in those who have the target condition relative to the odds of positivity in those without the condition |
*Expressed based on the notation used in table 1.