Likelihood ratios assess the probability or likelihood that the test result obtained would be expected in a person with the condition, compared to the probability or likelihood that the same result would be seen in a person without the condition (Deeks. 2001). The positive likelihood ratio 
expresses how many times more likely people with the condition are to receive a positive test result compared to those who do not have the condition, while the negative likelihood ratio 
expresses how likely it is that people with the condition will receive a negative test result compared to those who do not have the condition.
From the example presented in Table 9.2, 
The initial assessment of the likelihood of a disorder, that is the a priori probability, is modified by the results of the diagnostic test for a posteriori probability (the probability actually observed). A suggestion on the limited use of likelihood ratios is that their interpretation requires a calculator to convert between probabilities and odds of the disorder (McGee. 2002).