"A negative predictive value (NPV) is one of the four basic diagnostic test metrics in addition to sensitivity, specificity and positive predictive value. Negative predictive value is a measure of how often someone who tests negative for disease does not have disease and is calculated by dividing the number of true negatives (TN) by the number of people who tested negative, i.e. true negatives and false negatives (FN):"
"P(Disease negative |Test negative)"
"NPV = [(specificity) x (1 - p)] / [specificity x (1 - p) + (1 - sensitivity) x (p)]"