Likelihood Ratios (LR) : Introduction to Likelihood Ratios (LR) in Diagnostic Testing

In the field of diagnostic medicine, Likelihood Ratios (LRs) are valuable statistical measures used to assess the clinical utility of medical tests. LRs provide essential information about how much a particular test result (positive or negative) changes the likelihood of a patient having a specific medical condition. They help clinicians and researchers interpret test results more effectively and make informed decisions about patient care.

They provide a direct measure of how much a test result changes the odds of having a particular disease.

A likelihood ratio is defined as the ratio of the probability of a given test result in a patient with the disease to the probability of the same result in a patient without the disease. There are two types of likelihood ratios:

1. Positive likelihood ratio (LR+): This represents the increase in the probability of disease given a positive test result. A higher LR+ indicates that a positive test result is more likely to be true if the patient has the disease. It is calculated using the test's sensitivity (the proportion of true positives) and specificity (the proportion of true negatives).

2. Negative likelihood ratio (LR-): Conversely, LR- measures how much a negative test result decreases the likelihood of...