A lower negative likelihood ratio makes a negative test result more effective at what?

A lower negative likelihood ratio makes a negative test result more effective at what?

• A. Increases the probability the patient has the condition
• B. Decreases the probability the patient has the condition
• C. Has no effect on probability
• D. Only affects probability when pretest probability is high

Answer: (B)

A negative result with a small negative likelihood ratio dramatically reduces the odds that the patient has the condition. The post-test odds equal the pretest odds multiplied by the negative likelihood ratio. So when the LR- is very low, a negative test pushes the post-test probability downward more, making the test better at ruling out disease. In short, a lower LR- means a negative result is more effective at decreasing the probability of having the condition.

A negative result with a small negative likelihood ratio dramatically reduces the odds that the patient has the condition. The post-test odds equal the pretest odds multiplied by the negative likelihood ratio. So when the LR- is very low, a negative test pushes the post-test probability downward more, making the test better at ruling out disease. In short, a lower LR- means a negative result is more effective at decreasing the probability of having the condition.