Diagnostic test accuracy is simply the ability of the test to discriminate among alternative states of health (Zweig and Campbell, 1993).
If a test’s results do not differ between alternative states of health, then the test has insignificant accuracy; if the results do not overlap with other states of health then the test has perfect accuracy. Most tests accuracies fall between these two extremes.
The intrinsic accuracy of a test is measured by comparing the test results to the “true condition status.”
‘True condition status” refers to one of two mutually exclusive states. Either a condition is present or it is absent.
We determine true condition status by means of a “gold standard” which is a source of information completely different from the test under evaluation which tells us the true condition status of the patient.