Understanding Likelihood Ratios: A Simple Approach to Post-Test Probability

Earn 12.5 AMA PRA Category 1 Credits™ with the Core EM Modular CME Course. 12 curated EM modules with audio-first learning plus quizzes and downloadable resources. Start here: https://www.highmarksce.com/nyumc/Pla... — In this M.E.S.S. Mini (Making Evidence-Based Medicine Simple), we break down the concept of likelihood ratios—what they are, how to calculate them, and most importantly, how to use them in real-world clinical decision-making. You’ll learn: The strengths and limitations of likelihood ratios compared to sensitivity, specificity, and predictive values How to apply a likelihood ratio to a patient’s pre-test probability to estimate post-test probability How to interpret a CT scan for appendicitis using real-world data Why a likelihood ratio for a positive test greater than 10 and a likelihood ratio for a negative test less than 0.1 are considered strong, and how to rule in or rule out disease accordingly We also demonstrate tools like the Fagan Nomogram and an online calculator from the Centre for Evidence-Based Medicine to simplify the math behind diagnostic reasoning. Designed for clinicians who want to improve diagnostic accuracy using evidence-based tools.