These calculators and worksheets can be used in conjunction with the diagnoses and therapy cases.

Evidence-based medicine calculators

Diagnostic test equations 

 Disease presentDisease absent
Diagnostic test positive A B
Diagnostic test negative C D
  • Sensitivity = A / (A+C)
  • Specificity = D / (B+D)
  • Positive predictive value = A / (A+B)
  • Negative predictive value = D / (C+D)
  • LR (+) = [A / (A+C)] / [B / (B+D)] = sensitivity / (1-specificity)
  • LR (-) = [C / (A+C)] / [D / (B+D)] = (1-sensitivity) / specificity