Table 2

Definition of common measures of test accuracy

Test accuracy measureFormula*Definition
Sensitivitya/(a+c)Proportion of those with the target condition correctly identified as having the condition
Specificityd/(b+d)Proportion of those without the target condition correctly identified as not having the condition
Positive predictive valuea/(a+b)Proportion of those with the target condition out of the test positives
Negative predictive valued/(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 ORad/bc or LR+/LRRatio 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.