Of bombers, radiologists, and cardiologists: time to ROC

Assessing the accuracy of any diagnostic procedure remains integral to method evaluation. Evaluation of a diagnostic procedure is assessed by its ability to categorise patients accurately into those with or without a disease state. The presence or absence of the disease state is defined according to some, often arbitrarily selected “gold standard”. The nature of the gold standard can itself be a cause for debate. In the diagnosis of acute myocardial infarction (AMI), the gold standard has always been the criteria initially recommended by the WHO.1 2 As newer tests for AMI have been developed they have been evaluated against the gold standard and progressively replaced the older gold standard tests. Thus, aspartate aminotransferase (AST) measurement has been replaced by creatine kinase (CK). CK has been superseded by measurement of the more cardiac specific MB isoenzyme (CK-MB). Even in this case, as newer methods are developed for measuring CK-MB, mass measurements have replaced activity measurements to produce as the new gold standard the triad of chest pain, ECG changes, and CK-MB mass measurement. This results in a creeping diagnostic classification, the “gold” becoming purer (or perhaps less tarnished). Test accuracy is expressed in terms of sensitivity and specificity. The sensitivity of a test is defined as the ability to detect the diseased population. This equates to the number of real cases detected (referred to as true positives, TP) divided by the total number of cases in the population …