What does a positive likelihood ratio indicate?

A positive likelihood ratio indicates how much a positive test result increases the probability of disease. Specifically, it quantifies the likelihood that a person with the disease will have a positive test result compared to someone without the disease. A higher positive likelihood ratio means that a positive test result is much more likely in someone who has the disease than in someone who does not, thus providing valuable information for clinical decision-making.

This measure is particularly useful in determining the effectiveness of a diagnostic test. For instance, if the positive likelihood ratio is significantly greater than 1, it suggests that the test is helpful in diagnosing the disease. This metric plays a critical role in evidence-informed practice, helping clinicians to interpret test results and assess the need for further investigation or treatment effectively.

In contrast, the other options focus on different aspects of test performance or interpretation, such as the implications of negative results, the performance of tests in healthy populations, or the reliability of a test in a real-world setting, none of which directly address the meaning of a positive likelihood ratio.