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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

 
Input
 
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  

 
Results
 
Important: Inputs must be complete to perform calculation.

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

 
 

 
Notes
  • 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.

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Topic 13434 Version 10.0