LRs continued
The likelihood ratio is the probability of a patient with disease having a a particular finding divided by the probability of a patient without disease having the same finding.
The finding is either a positive test result (for positive likelihood ratios) or a negative test result (for negative likelihood ratios)
So: the positive likelihood ratio, then, is the probability of a patient with disease having a positive test result divided by the probability of patient without disease having a positive test result.
Test your understanding
In a good test, would the positive likelihood ratio be high or low?
And: the negative likelihood ratio, then, is the probability of a patient with disease having a negative test result divided by the probability of patient without disease having a negative test result.
Test your understanding
In a good diagnostic test, would the negative likelihood ratio be high or low?