Indices of efficacy

• Sensitivity = a/n1 = true positives/(true positives + false positives)
• Specificity = d/n2 = true negatives/(true negatives + false positives)
• Positive predictive value = a/m1 = true positives/(true positives + false positives)
• Negative predictive value = d/m2 = true negatives/(true negatives + false negatives)
• Accuracy = (a+d)/N = (true positives + true negatives/all individuals

Calculating the five main indices of efficacy

See Attributable fraction, Efficacy, False negative, False positive, Likelihood ration (LR), Precision, Sensitivity (epidemiology), Specificity (epidemiology)