Categories: Other Tips

Likelihood Ratios

Likelihood Ratio Approximate Change in Probability (%)*
Values between 0 and 1 decrease the probability of disease  
 0.1 −45
 0.2 −30
 0.3 −25
 0.4 −20
 0.5 −15
1 0
Values greater than 1 increase the probability of disease  
 2 +15
 3 +20
 4 +25
 5 +30
 6 +35
 7  
 8 +40
 9  
 10 +45

 

Easy to recall at the bedside by simply remembering 3 specific LRs—2, 5, and 10—and the first 3 multiples of 15 (i.e., 15, 30, and 45).

An LR of 2 increases probability 15%, one of 5 increases it 30%, and one of 10 increases it 45%. For those LRs between 0 and 1, the clinician simply inverts 2, 5, and 10 (i.e., 1/2 = 0.5, 1/5 = 0.2, 1/10 = 0.1).

Just as the LR of 2.0 increases probability 15%, its inverse, 0.5, decreases probability 15%. Similarly, an LR of 0.2 (the inverse of 5) decreases probability 30%, and a LR of 0.1 (the inverse of 10) decreases it 45%.

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Dr. C Humphreys

Internal Medicine

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