to determine the likelihood ratio

Test | given |
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not given |
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Positive Likelihood Ratio: | |

Negative Likelihood Ratio: |

The likelihood ratio for a test result compares the likelihood of that result in patients with disease to the likelihood of that result in patients without disease.

So how much do LRs change disease likelihood?

High LRs | Low LRs | Impact on Likelihood |

>10 | <0.1 | Large |

5-10 | 0.1-0.2 | Moderate |

2-5 | 0.2-0.5 | Small |

<2 | >0.5 | Tiny |

1 | 1 | No Change |

Positive Likelihood Ratio= (a/(a+c)) / (b/(b+d))

Negative Likelihood Ratio= (c/(a+c)) / (d/(b+d))

- or -

Positive Likelihood Ratio= (sensitivity)/(1-specificity) = TP/FP

Negative Likelihood Ratio= (1-sensitivity)/(specificity) = FN/TN

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