# * Email * Password Remember me

# Testing a Test

### The Two-By-Two Table

Test Result Present Absent Totals

 Positive True Positive a b False Positive a + b Negative True Negative c d False Negative c + d Totals a+c b+d a+b+c+d

Definitions and Calculations Related to Two-By-Two Table

Sensitivity - The proportion of individuals who have the disorder and test positive. Calculation: a/(a+c)

Specificity - the proportion of individuals who do not have the disorder and test negative. Calculation: d/(b+d)

Positive Predictive Value (PPV) - The proportion of individuals who test positive who have the disorder. Calculation: a/(a+b)

Negative Predictive Value (NPV) - The proportion of individuals who test negative who do not have the disorder. Calculation: d/(c+d)

Accuracy- the proportion of individuals who are correctly identified as either having or not having the disorder. Calculation (a+d)/(a+b+c+d)

Prevalence - The proportion of individuals in the sample who have the disorder. Calculation: (a+c)/(a+b+c+d)