The formula to calculate Likelihood Ratio is:
Positive Likelihood Ratio (LR+):
\[ LR+ = \frac{SE}{100 - SP} \]
Negative Likelihood Ratio (LR-):
\[ LR- = \frac{100 - SE}{SP} \]
Where:
A likelihood ratio is defined as the probability that a patient has a disease given the result of a test. The positive likelihood ratio (LR+) tells you how much to increase the probability of having a disease given a positive test result, while the negative likelihood ratio (LR-) tells you how much to decrease the probability given a negative test result.
Let's consider an example:
Using the formula to calculate Likelihood Ratios:
Positive Likelihood Ratio (LR+):
\[ LR+ = \frac{90}{100 - 80} = 4.5 \]
Negative Likelihood Ratio (LR-):
\[ LR- = \frac{100 - 90}{80} = 0.125 \]
This demonstrates that with a sensitivity of 90% and a specificity of 80%, the positive likelihood ratio would be 4.5 and the negative likelihood ratio would be 0.125.
