Diagnostic value of a diagnostic test
For sub-studies focusing on the diagnostic value of a particular diagnostic test, the negative predictive value (NPV), positive predicted value (PPV), sensitivity and specificity will be calculated. The NPV represents the number of true negatives divided by the negative calls (true negative + false negative). The PPV is the number of true positives divided by the positive calls. Sensitivity is the proportion of people who test positive among all those who actually have the disease and is calculated by dividing the true positive by the true positive plus false negative. Specificity is the proportion of people who test negative among all those who actually do not have that disease, and is calculated by dividing the true negative and the true negative plus false positive.