What does a negative likelihood ratio describe?

A negative likelihood ratio is a statistical measure used to understand the usefulness of a diagnostic test. Specifically, it describes how much a negative test result decreases the probability of a disease being present in a patient. This ratio is calculated by taking the probability of a negative test result in patients with the disease and dividing it by the probability of a negative test result in patients without the disease.

When the negative likelihood ratio is low, it suggests that a negative test result is very effective at ruling out the disease, as it indicates that a person is less likely to have the disease given a negative test result. Conversely, a high negative likelihood ratio suggests that a negative test result does not significantly diminish the probability of disease.

Understanding this concept is crucial for healthcare practitioners when interpreting test results, as it aids in clinical decision-making and the assessment of patient risk.