based on example shown in Evidence-based Medicine (Sackett, Richardson,Rosenberg,Haynes) page 120, Churchill Livingstone, publishers.
Diagnostic Test |
Target Disorder |
|
Present | Absent | |
Positive | a | b |
Negative | c | d |
Sensitivity = a/(a+c) | |
Specificity = d/(b+d) | |
LR+ = sensitivity/(1-specificity) | |
LR-= (1-sensitivity)/specificity | |
Positive predictive value = a/(a+b) | |
Negative predictive value = d/(c+d) | |
Prevalence = (a+c)/(a+b+c+d) | |
Pretest odds = prevalence/(1-prevalence) | |
Post-test odds = pretest odds * likelihood ratio | |
Post-test probability (%) = post-test odds/(post-test odds +1) |