Why do we use likelihood ratios with a nomogram for our predictive index?
Likelihood ratios, (LR), are key concepts in the interpretation of diagnostic test results. They combine the information in both sensitivity and specificity into a more meaningful number. The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic test or sequence of tests. They have advantages over sensitivity and specificity alone because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the test result, most importantly, they can be used to combine the results of multiple diagnostic tests which then can be used to calculate a post-test probability for a target disorder. See our Clinical manual or the ROC of PADDS page for a more complete description.
