What is a likelihood ratio?
The likelihood ratio provides a direct estimate of how much a test result will change the odds of having a disease, and incorporates both the sensitivity and specificity of the test.
The likelihood ratio for a positive result (LR+) tells you how much the odds of the disease increase when a test is positive.
The likelihood ratio of a positive test result (LR+) is sensitivity divided by (1 specificity)

The likelihood ratio for a negative result (LR) tells you how much the odds of the disease decrease when a test is negative.

Interpretation of Likelihood Ratios
The further away a likelihood ratio (LR) is from 1, the stronger the evidence for the presence or absence of disease.
 LR >1 indicates that the test result is associated with the presence of the disease.
 LR <0.1 indicates that the test result is associated with the absence of disease.
© Dr Murad Ruf and Dr Oliver Morgan 2008, Dr Kelly Mackenzie 2017