Likelihood Ratio Calculator

Real-Time Diagnostic Test Analysis Tool

Real-Time

Diagnostic Test Parameters

%
Probability that test is positive when disease is present
%
Probability that test is negative when disease is absent
%
Prevalence or clinical suspicion before test
Select whether test result is positive or negative

Real-Time Calculation Results

Positive Likelihood Ratio (LR+)
7.65
How much the odds of disease increase with a positive test
Negative Likelihood Ratio (LR-)
0.19
How much the odds of disease decrease with a negative test
Pre-Test Probability
20.0%
Probability of disease before test
Post-Test Probability
65.7%
Probability of disease after test result
Clinical Interpretation

A positive test result increases the probability of disease from 20% to 65.7%. The positive likelihood ratio of 7.65 indicates a moderately useful test for ruling in the disease when positive.

Strength of Evidence: Moderate

Tool Features

Key Functionalities:
Real-Time Calculation Dual Input Controls LR+ & LR- Calculation Pre/Post-Test Probability Clinical Interpretation Calculation History Export Results Educational Guidance Print Reports Share Tool
Quick Actions:
Recent Calculations
Sens: 85%, Spec: 90%, Pre: 20%
LR+: 7.65 Just now

How to Use the Likelihood Ratio Calculator

This likelihood ratio calculator helps healthcare professionals and researchers evaluate diagnostic tests by calculating positive and negative likelihood ratios (LR+ and LR-) along with post-test probabilities.

Step-by-Step Guide:
  1. Enter Sensitivity: Input the test's sensitivity (true positive rate) as a percentage. This is the probability that the test correctly identifies individuals with the disease.
  2. Enter Specificity: Input the test's specificity (true negative rate) as a percentage. This is the probability that the test correctly identifies individuals without the disease.
  3. Set Pre-Test Probability: Enter the estimated probability of disease before testing (prevalence or clinical suspicion).
  4. Select Test Result: Choose whether the test result is positive or negative.
  5. Review Results: The calculator instantly displays LR+, LR-, and post-test probability with clinical interpretation.
Understanding Likelihood Ratios:
  • LR+ (Positive Likelihood Ratio): Values greater than 1 increase the probability of disease. Higher values indicate better tests.
  • LR- (Negative Likelihood Ratio): Values less than 1 decrease the probability of disease. Values closer to 0 indicate better tests.
  • Post-Test Probability: The updated probability of disease after considering the test result.
Clinical Tip:

Likelihood ratios are more useful than sensitivity and specificity alone because they incorporate pre-test probability to give a post-test probability that is clinically actionable.

LR Interpretation Guide
  • LR+ > 10 Large increase
  • LR+ 5-10 Moderate increase
  • LR+ 2-5 Small increase
  • LR+ 1-2 Minimal increase
  • LR- 0.5-1 Minimal decrease
  • LR- 0.2-0.5 Small decrease
  • LR- 0.1-0.2 Moderate decrease
  • LR- < 0.1 Large decrease