Table 8.

Measures to assess diagnostic accuracy of imaging methods and description of measures

Measure	Description
Sensitivity: true positive rate	The probability that the index test correctly identifies those with the target condition (compared to the reference standard) The percentage of true positive test results found in the group that actually has the target condition
Specificity: true negative rate	The probability that the index test correctly rules out those without the target condition (compared to the reference standard) The percentage of true negative test results found in the group that is actually healthy
Positive predictive value (PV+)	True positive test results as a percentage of all positive test results (true positives/true positives + false positives); the probability that a positive test result is correct False positive cases may be termed “false alarm cases”
Negative predictive value (PV-)	True negative test results as a percentage of all negative test results (true negatives/true negatives + false negatives); the probability that a negative test result is correct False negative cases may be termed “missed cases”
Likelihood ratios (LRs)	Indicates the clinical value of the index test If the LRs are close to 1.0 the index test is of little value
Positive likelihood ratio (LR+)	The odds of correctly identifying those with the target condition versus false alarms, i.e.. sensitivity/(1- specificity)
Negative likelihood ratio (LR-)	The odds of missing cases versus correctly ruling out those with the target condition, i.e. (1- sensitivity)/specificity
Receiver Operating Characteristic (ROC)	The relation between the true-positive rate and the false-positive rate at usually five threshold steps