Enter the sensitivity and specificity into the calculator to determine the likelihood ratio.

Likelihood ratio Formula

The following formula is used to calculate a likelihood ratio.

Positive LR = SE / (100- SP) 
Negative LR = (100 - SE) / SP 
  • Where LR is the likelihood ratio
  • SE is the sensitivity
  • SP is the specificity

To calculate a positive likelihood ratio, divide the sensitivity by 100 minus the specificity.

In this case, the positive LR tells you how much to increase the probability of having a disease given that someone receives a positive disease test result. Negative LR tells you how much to decrease the probability given a negative test result.

Likelihood Ratio Definition

A likelihood is defined as the probability that a patient has a disease given the result of a test.

Likelihood Ratio Example

How to calculate a likelihood ratio?

  1. First, determine the sensitivity.

    Calculate or measure the sensitivity of the specific test.

  2. Next, determine the the specificity.

    Calculate or measure the specificity of the test.

  3. Finally, calculate the likelihood ratio.

    Calculate the ratio using the equation above.


What is a likelihood ratio?

A likelihood ratio describes the rate or chance that a person has a condition given the result of a specific test.