Important Biostatistics and Epidemiology Equations



Sensitivity = TP / (TP + FN) = true positives / disease present

Specificity = TN / (FP + TN) = true negatives / disease absent



Positive Predictive Value = TP / (TP + FP) = true positives / all positives

Negative Predictive Value = TN / (FN + TN) = true negatives / all negatives



Positive Likelihood Ratio = Sensitivity / (1 – Specificity)

Negative Likelihood Ratio = (1 – Sensitivity) / Specificity



Sensitivity vs Specificity Mnemonic: 

 - Sensitivity = SNOUT = Rule OUT

 - Specificity = SPIN = Rule IN



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