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Likelihood ratio ( LR )

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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  • this is defined as the ratio of the probability of a test result among patients with a target disorder to the probability of that same test result among patients who do not have the target disorder
  • the likelihood ratio for a positive test is calculated as:
    sensitivity / (1-specificity)
  • the likelihood ratio of a negative result is calculated as:

Note that sensitivity = (a/[a+c]) and

specificity = (d/[b+d])


target disorder present

target disorder absent

test result positive



test result negative





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