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. | ||
:<math>\text{Likelihood ratio} = \frac{\mbox{probability of test result with disease}}{\mbox{probability of same result without disease}}</math> | |||
:<math>\text{Likelihood ratio} = \frac{\mbox{sensitivity}}{1 - \mbox{specificity}}</math> | |||
To calculate probabilities of disease using a likelihood ratio: | |||
:<math>\text{Post-test odds} = \text{Pre-test odds} * \text{Likelihood}\ \text{ratio}</math> | |||
Comparing likelihoods (or odds) is different than comparing percentages. (or probabilities). | |||
:<math>\text{Odds}=\frac{\text{probability}}{(1-\text{probability})}</math> | |||
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> | 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> | ||
==Calculations== | ==Calculations== | ||
Likelihood ratios are | Likelihood ratios are related 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.<ref name="pmid12213147">{{cite journal |author=McGee S |title=Simplifying likelihood ratios |journal=J Gen Intern Med |volume=17 |issue=8 |pages=646–9 |year=2002 |month=August |pmid=12213147 |doi= |url= |issn=}}</ref> | 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.<ref name="pmid12213147">{{cite journal |author=McGee S |title=Simplifying likelihood ratios |journal=J Gen Intern Med |volume=17 |issue=8 |pages=646–9 |year=2002 |month=August |pmid=12213147 |doi= |url= |issn=}}</ref> | ||
<math>\text{LR+} = \frac{\text{sensitivity}}{(1-\text{specificity})}</math> | :<math>\text{LR+} = \frac{\text{sensitivity}}{(1-\text{specificity})}</math> | ||
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.<ref name="pmid12213147">{{cite journal |author=McGee S |title=Simplifying likelihood ratios |journal=J Gen Intern Med |volume=17 |issue=8 |pages=646–9 |year=2002 |month=August |pmid=12213147 |doi= |url= |issn=}}</ref> | 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.<ref name="pmid12213147">{{cite journal |author=McGee S |title=Simplifying likelihood ratios |journal=J Gen Intern Med |volume=17 |issue=8 |pages=646–9 |year=2002 |month=August |pmid=12213147 |doi= |url= |issn=}}</ref> | ||
<math>\text{LR-} = \frac{(1-\text{sensitivity})}{\text{specificity}}</math> | :<math>\text{LR-} = \frac{(1-\text{sensitivity})}{\text{specificity}}</math> | ||
==References== | ==References== | ||
<references/> | <references/> | ||
Revision as of 21:46, 15 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.
To calculate probabilities of disease using a likelihood ratio:
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 related 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]