1. What is Likelihood Ratio?

The Likelihood Ratio (LR+) is a measure of how much a positive test result changes the odds of having a condition. It compares the probability of a positive test result in people with the disease to those without the disease.

2. How Does the Calculator Work?

The calculator uses the Likelihood Ratio formula:

Where:

• \( Sensitivity \) — True positive rate (0-1)
• \( Specificity \) — True negative rate (0-1)

Explanation: The LR+ tells us how much more likely a positive test result is in people with the disease compared to those without it.

3. Importance of Likelihood Ratio

Details: LR+ is crucial for interpreting diagnostic tests. Higher values indicate better test performance:

• LR+ > 10: Large and often conclusive increase in likelihood of disease
• LR+ 5-10: Moderate increase in likelihood
• LR+ 2-5: Small increase in likelihood
• LR+ 1-2: Minimal increase in likelihood

4. Using the Calculator

Tips: Enter sensitivity and specificity as values between 0 and 1 (e.g., 0.95 for 95%). Both values must be valid (between 0-1).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between LR+ and LR-?
A: LR+ is for positive test results, while LR- is for negative results (calculated as (1-sensitivity)/specificity).

Q2: How do I interpret an LR+ value?
A: Multiply the pre-test odds by LR+ to get post-test odds. Higher values mean the test is better at ruling in disease.

Q3: What's a good LR+ value?
A: Generally, LR+ >10 is excellent, 5-10 is good, 2-5 is fair, and <2 provides little diagnostic value.

Q4: Can LR+ be less than 1?
A: Yes, but this indicates the test is worse than chance at identifying the condition.

Q5: How does LR+ relate to predictive values?
A: Unlike predictive values, LR+ is independent of disease prevalence, making it more generalizable.