Home>Domains-Diagnosis-Calculations
Diagnostic Tests
Calculators
Centre for Evidence Based Medicine Stats Calculator
Vanderbilt- Power and Sample Size Calculator
Gold standard Positive (condition present) |
Gold standard Negative (condition not present) | |
Test result Positive | True Positive |
False Positive |
Test result Negative | False Negative |
True Negative |
Stable Properties:
Sensitivity = True Positives/(True Positives + False Negatives)
Specificity = True Negatives/(False Positive + True Negative)
Frequency Dependent Properties:
Positive Predictive Value = True Positive/(True Positive + False Positive)
Negative Predictive Value = True Negative/(True Negative + False Negative)
The likelihood ratio for a test result compares the likelihood of that result in patients with disease to the likelihood of that result in patients without disease:
Condition Present |
Condition Absent |
|
Test Positive | a |
b |
Test Negative | c |
d |
Positive LR = (a/a+c)/(b/b+d)
Negative LR = (c/a+c)/(d/b+d)
How much do Likelihood Ratios change disease likelihood?
LRs >10 or <0.1 cause large changes in likelihood.
LRs 5-10 or 0.1-0.2 cause moderate changes.
LRs 2-5 or 0.2-0.5 cause small changes.
LRs between <2 and 0.5 cause little or no change.