Comparing diagnostic tests: a simple graphic using likelihood ratios

The diagnostic abilities of two or more diagnostic tests are traditionally compared by their respective sensitivities and specificities, either separa tely or using a summary of them such as Youden's index. Several authors hav e argued that the likelihood ratios provide a more appropriate, if in pract ice a less intuitive, comparison. We present a simple graphic which incorpo rates all these measures and admits easily interpreted comparison of two or more diagnostic tests. We show, using likelihood ratios and this graphic, that a test can be superior to a competitor in terms of predictive values w hile having either sensitivity or specificity smaller. A decision theoretic basis for the interpretation of the graph is given by relating it to the t ent graph of Hilden and Glasziou (Statistics in Medicine, 1996). Finally, a brief example comparing two serodiagnostic tests for Lyme disease is prese nted. Published in 2000 by John Wiley & Sons, Ltd.