Patient-oriented performance measures of diagnostic tests. 1. Tools for prospective evaluation of test order...

Prospective assessment of a test for possible use in evaluation of a patient ideally should be based on the test's ability to affect subsequent patient management beneficially, in relation to both the costs of the test itself and the costs of misclassification of disease status. This requires specification of the costs and benefits of subsequent actions and the cost of the test, estimation of the probability of disease, knowledge of the discriminatory properties of the test, and formal decision analysis. Often, however, the physician has less complete information with which to make a test order decision. A spectrum of performance measures exists for characterising a diagnostic test, ranging from measures that are largely patient-independent to measures that are highly patient-dependent. Two measures from the patient-dependent part of the spectrum, Assignment Potential and Assignment Strength, can be useful in decision making when formal decision analysis is not feasible. A third measure, the U-Factor, is the product of the other two, and is a computational tool that facilitates formal decision analysis.