Dichotomous diagnostic decision: D+= disease present; D- , disease absent.
Dichotomous test: T+, " positive" test result suggesting presence of disease; T- , "negative" test result suggesting absence of the disease*.
True disease status of the subjects investigated must be verified by a method independent from the diagnostic test under scrutiny.
The probabilities of finding a positive or negative test result in case of presence or absence of disease are constant and independent from the population investigated.
* In clinical chemistry often by transforming results into a dichotomous variable comparing it with a treshold (cut-off value) and indicating whether is lies below or above this limit.