# likelihood ratio

^{33Deeks JJ. Systematic reviews of evaluations of diagnostic and screening tests. In: Egger M, Davey Smith G, Altman DG, editors. Systematic reviews in health care: meta-analysis in context. 2nd ed. London: BMJ Books; 2001. p. 248-82. Reference details: }

^{34Porta M (ed). A Dictionary of Epidemiology. Sixth edition. A Handbook for the International Epidemiological Association. Oxford: Oxford University Press, 2014 Reference details: }

A measure of the strength of a diagnostic test to distinguish between persons who do or do not have a target condition.

**Note 1: **A positive likelihood ratio compares the probability of a positive test result in persons with the disease with the probability of a positive test result in persons without the disease. A negative likelihood ratio compares the probability of a negative test result in persons without the disease with the probability of a negative test result in persons with the disease.
**Note 2: **Positive likelihood ratios greater than 10 or negative likelihood ratios less than 0.1 are sometimes judged to provide convincing diagnostic evidence.
**Note 3: **A positive likelihood ratio is calculated as: sensitivity ÷ (1 minus specificity). A negative likelihood ratio is calculated as: (1 minus sensitivity) ÷ specificity.
**Note 4: **In statistics, an alternative meaning of the* likelihood ratio *exists. It is the ratio of the values of the likelihood function at two different parameter values or under two different data models. See also *likelihood ratio test*.