
Prior probability (odds): 
31% (0.5) 

POSITIVE TEST: 
Positive Likelihood ratio: 
1.44 
95% confidence interval: 
[1.18,1.75] 
Posterior probability (odds): 
40% (0.7) 
95% confidence interval: 
[35%,44%] 
(~ 1 in 2.5 with positive test 
are sick) 

NEGATIVE TEST: 
Negative Likelihood ratio: 
0.24 
95% confidence interval: 
[0.08,0.72] 
Posterior probability (odds): 
10% (0.1) 
95% confidence interval: 
[4%,25%] 
(~ 1 in 1.1 with negative test 
are well) 

Odds = Probability / (1Probability) 
+LR = Sensitivity / (1  Specificity) 
LR = (1  Sensitivity) / Specificity 
Posterior Odds = Prior Odds x LR 
