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Arch Hellen Med, 23(1), January-February 2006, 84-91


Diagnostic quality. Likelihoods


Laboratory of Clinical Epidemiology, School of Nursing, University of Athens, Athens, Greece

The clinical usefulness of a diagnostic test (laboratory test or clinical finding) is determined by the discriminating ability of the test, meaning its ability to correctly classify patients with or without a specified disease. The most commonly used measures of the diagnostic value of a test are the true positive rate or sensitivity (proportion of people with the disease who have a positive test result) and the true negative rate or specificity (proportion of people without the disease who have a negative test result). These and their complementary rates, the false negative rate (proportion of people with the disease who have a negative test result) and the false positive rate (proportion of people without the disease who have a positive test result), respectively, are called the likelihoods or the operating characteristics of the diagnostic test. The diagnostic properties of a test may be inaccurately described because an inappropriate gold standard has been chosen. Also, the spectrum of patients (stage, severity, duration of disease) used to describe the properties of the test and the bias in judging the performance of the test can affect the determination of the true positive and false positive rates. These biases tend to make the test seem more useful than it actually is.

Key words: Discriminating ability, Likelihood, Operating characteristics, Sensitivity, Specificity.

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