Likelihood Ratios: พื้นฐานความน่าจะเป็นในเชิงเงื่อนไข (Conditional Probability)

🔶 LR⁺ (Likelihood Ratio for a Positive Test)

📌 Definition

The ratio of the probability of a positive test in someone with the disease to the probability of a positive test in someone without the disease.

🧠 Clinical Interpretation:

LR⁺ tells how much more likely a positive result is in someone with the disease than in someone without the disease.

• LR⁺ > 10 → Strong evidence for ruling in disease

• LR⁺ ~1 → Test is not useful for confirmation

Structure for LR + :

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🔷 LR⁻ (Likelihood Ratio for a Negative Test)

📌 Definition

The ratio of the probability of a negative test in someone with the disease to the probability of a negative test in someone without the disease.

🧠 Clinical Interpretation:

LR⁻ tells how much more likely a negative result is in someone with the disease than in someone without the disease.

• LR⁻ < 0.1 → Strong evidence for ruling out disease

• LR⁻ ~1 → Test is not helpful in exclusion

Structure for LR - :