Interval likelihood ratios: Another advantage for the evidence-based diagnostician

Nomogram for interpreting diagnostic test results. Place a straight edge on the left side of the figure at a point corresponding to an estimate of the probability of a disease before the performance of a test. Connect that point to the likelihood ratio corresponding to the test result in the middle of the figure. The point of intersection of the straight edge with the right-hand side of the figure corresponds to the probability of the disease implied by the test result. Adapted from Fagan TJ. Nomogram for Bayes theorem [letter]. N Engl J Med. 1975;293:257. Copyright © 1975 Massachusetts Medical Society. All rights reserved.¹¹

An example of the calculation of interval likelihood ratios from an ROC curve for B-type natriuretic peptide as a predictor of cardiac events in patients with congestive heart failure. BNP, B-type natriuretic peptide. Adapted from Harrison A, Morrison LK, Krishnaswamy P, et al. B-type natriuretic peptide predicts future cardiac events in patients presenting to the emergency department with dyspnea.Ann Emerg Med. 2002;39:131-138.Reprinted with permission.⁹