Sensitivity = a/(a+c) 

Specificity = d/(b+d) 

LR+ = sensitivity/(1specificity) 

LR= (1sensitivity)/specificity 

Positive predictive value = a/(a+b) 

Negative predictive value = d/(c+d) 

Prevalence = (a+c)/(a+b+c+d) 

Pretest odds = prevalence/(1prevalence) 

Posttest odds = pretest odds * likelihood
ratio 

Posttest probability (%) = posttest
odds/(posttest odds +1) 
