likelihood ratio (LR)

Introduction

Change in odds of disease for a test result. An LR of > 1 makes disease more likely. An LR of < 1 makes disease less likely. defined as:

probability of obtaining result in patient with specified disease /
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probability of obtaining result in patient without specified disease

In the case of dichotomous results:

LR associated with abnormal test (positive LR): sensitivity/(1-specificity)

LR associated with normal test (negative LR): (1-sensitivity)/specificity

positive LR of 2, 5, & 10 increase probability of disease by ~ 15%, 30%, & 45% respectively.

For example, if the pretest probablity of a condition is 50%, a likelihood ratio of 10 yields a post-test probability of 95% (50% + 45% = 95%).

negative LR of 0.5, 0.2, & 0.1 decrease probability of disease by ~ 15%, 30%, & 45% respectively.

For example, if the pretest probablity of a condition is 50%, a likelihood ratio of 0.1 yields a post-test probability of 5% (50% - 45% = 5%)

More general terms

• statistics (biostatistics)