Module 11c Likelihood Ratios & Pretest/Posttest Probability

The goal of this session is to to learn how to define and calculate likelihood ratios, and use them to calculate and interpret pretest/posttest probabilities. Likelihood ratios are used to assess how good a diagnostic test is and to help in selecting appropriate diagnostic test(s). LRs have advantages over PPV and NPV because they are less likely to change with the prevalence of the disorder. LRs can be calculated for several levels of the symptom/sign or test. LRs can be used to calculate posttest probability for a disease of interest. Bayesian statistics is a field of statistics in which prior beliefs are quantified as pretest probabilities and combined with the LR to calculate posttest probabilities. Allow interpretation of clinical screening or diagnostic tests within their clinical context.