Patient-oriented performance measures of diagnostic tests. 3. U-Factor.

When a clinician is faced with the problem of deciding whether to order a specific diagnostic test, the ideal information would be the utility of the "perform test" branch of the decision tree versus the utility of the "do not perform test" branch. This difference in utility is termed the Expected Utility of the Test ( EUT ). We propose a new performance measure of a test called the U-Factor (UF) which is related to EUT by a simple formula. UF depends on the prior probability of disease and on the decision thresholds at which one would be indifferent between any two immediately subsequent management options, and can be presented as a two-dimensional nomogram. UF is useful as a computational aid in a formal decision analysis, and may be useful as an informal measure of the value of a diagnostic test when a formal analysis is not feasible.