SCREENING TEST

True Positive (a) = Test (+) Disease (+)
False Positive (b) = Test (+) Disease (-)
False Negaive (c) = Test (-) Disease (+)
True Negative (d) = Test (-) Disease (-)

Accuracy = (True Positive + True Negative) / (Total)
Precision = (True Positive) / (True Positive + False Positive)

[http://gotoknow.org/blog/epistat/393264]

	Gold Standard
	Dis (+)	Dis (-)
Test (+)	a	b
Test (-)	c	d

			Percent
Sensitivity	TP/(TP+FN)	a/(a+c)
Specificity	TN/(FP+TN)	d/(b+d)
PPV	TP/(TP+FP)	a/(a+b)
NPV	TN/(FN+TN)	d/(c+d)