## Interpreting Likelihood Ratios **Key Point:** Likelihood ratios quantify how much a test result shifts the probability of disease from the pre-test probability (prior odds). LR+ indicates ruling-in power; LR− indicates ruling-out power. ### Interpretation Scale | LR Value | Interpretation | Clinical Utility | |----------|----------------|------------------| | LR+ > 10 | Very strong evidence for disease | **Excellent for ruling IN** | | LR+ 5–10 | Strong evidence for disease | Good for ruling in | | LR+ 2–5 | Moderate evidence for disease | Moderate for ruling in | | LR+ 1–2 | Weak evidence for disease | Poor for ruling in | | LR− < 0.1 | Very strong evidence against disease | **Excellent for ruling OUT** | | LR− 0.1–0.2 | Strong evidence against disease | Good for ruling out | | LR− 0.2–0.5 | Moderate evidence against disease | Moderate for ruling out | | LR− 0.5–1 | Weak evidence against disease | Poor for ruling out | ### Analysis of This Test **Positive Likelihood Ratio (LR+) = 10:** - Falls in the "excellent" range (> 10) - A positive test result is 10 times more likely in patients WITH disease than WITHOUT disease - **Conclusion:** Positive result strongly rules IN disease **Negative Likelihood Ratio (LR−) = 0.1:** - Falls in the "excellent" range (< 0.1) - A negative test result is 0.1 times as likely (i.e., 10 times less likely) in patients WITH disease than WITHOUT disease - **Conclusion:** Negative result strongly rules OUT disease **High-Yield:** LR+ > 10 and LR− < 0.1 represent the gold standard for diagnostic test performance — the test is both highly sensitive and highly specific. **Mnemonic:** **SnNOut, SpPIn** - **Sn**Nout: High **Sensitivity** + **Negative** result = rules OUT disease - **Sp**PIn: High **Specificity** + **Positive** result = rules IN disease This test achieves both: LR− < 0.1 (high sensitivity) and LR+ > 10 (high specificity).
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