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For a screening or diagnostic test (including clinical signs or symptoms), the likelihood ratio (LR) expresses the relative likelihood that a given...
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For a screening or diagnostic test (including clinical signs or symptoms), the likelihood ratio (LR) expresses the relative likelihood that a given test would be expected in a patient with, as opposed to one without, a disorder of interest. An LR of 1 means that the posttest probability is identical to the pretest probability. As LRs increase above 1, the posttest probability progressively increases in relation to the pretest probability. As LRs decrease below 1, the posttest probability progressively decreases in relation to the pretest probability. An LR is calculated as the proportion of target positive with a particular test result (which, with a single cut point, would be either a positive or negative result) divided by the proportion of target negative with same test result.