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Calculator: Post-test probability from likelihood ratios and multiple test results

Calculator: Post-test probability from likelihood ratios and multiple test results

Pre-test probability  
Test 1 Not done   Positive   Negative  
Test 1 LR positive  
Test 1 LR negative  
Test 2 Not done   Positive   Negative  
Test 2 LR positive  
Test 2 LR negative  
Test 3 Not done   Positive   Negative  
Test 3 LR positive  
Test 3 LR negative  

Important: Inputs must be complete to perform calculation.

Pre-test odds  
Post-test odds  
Post-test probability  
Decimal precision  


  • Use this calculator to evaluate the contribution of different test results to an overall Post-test probability of a disease or condition based on the Pre-test probability (prevalence) and the likelihood ratios of the various tests employed.
  • Input one or more test results and the associated LR positive and LR negative values associated with that test.
  • When a test result is positive, only the LR positive input is required. If a test result is negative, only the LR negative input is required.
  • This calculator then mutiplies the appropriate likelihood ratios by the Pre-test odds to produce the Post-test odds.
  • The Post-test odds are then converted to an overall Post-test probability.
  • Positive likelihood ratio: (Test sensitivity/(1 - test specificity); negative likelihood ratio: (1 - test sensitivity)/test specificity).
  • LR: likelihood ratio.

Equations used
Pre-test odds = Pre-test probability / (1 - Pre-test probability)
Post-test odds = Overall_Odds
Post-test probability = Post-test odds / (1 + Post-test odds)


Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

Information on this page may not appear correctly if printed.

Legal Notices and Disclaimer

All information contained in and produced by the EBMcalc system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER. Click here for full notice and disclaimer.

EBMcalc is Copyright © 1998-2023 Foundation Internet Services, LLC

Topic 13434 Version 10.0