Positive likelihood ratio

Positive likelihood ratio

The positive likelihood ratio (LR+) is a statistical measure used in diagnostic testing in medicine. It is the ratio of the probability of a positive test result given the presence of the disease to the probability of a positive test result given the absence of the disease.

Definition

The positive likelihood ratio is defined as:

LR+ = Sensitivity / (1 - Specificity)

where Sensitivity is the probability of a positive test result given the presence of the disease, and Specificity is the probability of a negative test result given the absence of the disease.

Interpretation

The LR+ is interpreted as follows:

• An LR+ greater than 1 increases the probability of disease.
• An LR+ less than 1 decreases the probability of disease.
• An LR+ of 1 means the test does not change the probability of disease.

Use in medicine

In medicine, the LR+ is used to assess the value of a diagnostic test. It is particularly useful in situations where the disease prevalence is low, as it provides a measure of the increase in probability of disease given a positive test result.

See also

• Negative likelihood ratio
• Receiver operating characteristic
• Sensitivity and specificity

Positive likelihood ratio Resources
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