Likelihood ratio: Difference between revisions
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In [[diagnostic test]]s, the '''likelihood ratio''' is the likelihood that a clinical [[sign (medical)|sign]] is in a patient with disease as compared to a patient without disease. Comparing likelihoods (or odds) is different than comparing percentages. (or probabilities). | In [[diagnostic test]]s, the '''likelihood ratio''' is the likelihood that a clinical [[sign (medical)|sign]] is in a patient with disease as compared to a patient without disease. Comparing likelihoods (or odds) is different than comparing percentages. (or probabilities). | ||
The likelihood ratio is an alternative to [[sensitivity and specificity]] for the numeric interpretation of [[diagnostic test]]s. In a [[randomized controlled trial]] that compared the two methods, physicians were able to use both similarly although the physicians had trouble with both methods.<ref name="pmid16061916">{{cite journal |author=Puhan MA, Steurer J, Bachmann LM, ter Riet G |title=A randomized trial of ways to describe test accuracy: the effect on physicians' post-test probability estimates |journal=Ann. Intern. Med. |volume=143 |issue=3 |pages=184–9 |year=2005 |month=August |pmid=16061916 |doi= |url= |issn=}}</ref> | |||
<math>\text{Odds}=\frac{\text{probability}}{(1-\text{probability})}</math> | <math>\text{Odds}=\frac{\text{probability}}{(1-\text{probability})}</math> | ||
Revision as of 12:16, 14 April 2009
In diagnostic tests, the likelihood ratio is the likelihood that a clinical sign is in a patient with disease as compared to a patient without disease. Comparing likelihoods (or odds) is different than comparing percentages. (or probabilities).
The likelihood ratio is an alternative to sensitivity and specificity for the numeric interpretation of diagnostic tests. In a randomized controlled trial that compared the two methods, physicians were able to use both similarly although the physicians had trouble with both methods.[1]
Calculations
Likelihood ratios are relatived to sensitivity and specificity.
The positive likelihood ratio (LR+) measures the likelihood of a finding being present in patient with the disease. A large LR+, for example a value more than 10, helps rule in disease.[2]
The negative likelihood ratio (LR-) measures the likelihood of a finding being absent in patient with the disease. A small LR-, for example a value less than 0.1, helps rule out disease.[2]
References
- ↑ Puhan MA, Steurer J, Bachmann LM, ter Riet G (August 2005). "A randomized trial of ways to describe test accuracy: the effect on physicians' post-test probability estimates". Ann. Intern. Med. 143 (3): 184–9. PMID 16061916. [e]
- ↑ 2.0 2.1 McGee S (August 2002). "Simplifying likelihood ratios". J Gen Intern Med 17 (8): 646–9. PMID 12213147. [e]