Bayes' Diagnostic Ruler

Diagnostic probability calculator by Dr Richard Haydon, Emergency Physician, Melbourne

Probability scale · log-odds
i
False reassuranceOver treatment
−ve test (LR−)()
Prior
+ve test (LR+)()

1. Prior probability

0.1%50%99.9%

2. Apply evidence

Sensitivity
Specificity
LR+
1×10×100× (type higher, or ∞)
LR−
0.01×0.1×1×
Sensitivity
Specificity
Lock:
Positive LR (LR+)Sens / (1 − Spec)
Negative LR (LR−)(1 − Sens) / Spec
Show plot
00.51 00.51 1 − SpecificitySensitivity
Sensitivity🔒
Specificity🔒
LR+🔒
LR−🔒

The red line is the LR+ line, its slope equals LR+. The green line is the LR− line, its slope equals LR−. They cross at this test's sensitivity and specificity. The top-left corner is a perfect test; the dashed diagonal is a useless test (LR 1). Drag the point to change sensitivity and specificity.