Table 4.

Statistics used in evaluating diagnostic accuracy study results

Statistic	Definition	Formula †
Overall accuracy	Proportion of correct test results	(A + D)/(A + B + C + D)
Sensitivity	Probability of a positive test result in an individual with the condition	A/(A + C)
Specificity	Probability of a negative test result in an individual without the condition	D/(B + D)
Positive predictive value	The probability of having the condition when the test result is positive	A/(A + B)
Negative predictive value	The probability of not having the condition when the test result is negative	D/(C + D)
Positive likelihood ratio	Increase in odds favoring the condition when the test result is positive	Sensitivity/(1−specificity)
Negative likelihood ratio	Decrease in odds favoring the condition when the test result is negative	(1−sensitivity)/specificity

^†Formulas are based on parameters in table 3