Herd X, n = 400 cows				Herd Y, n = 400 cows
	D+	D−			D+	D−
T+	60	2	62	T+	10	2	12
T−	60	278	338	T−	10	378	388
	120	280	400		20	380	400

Negative predictive value: Herd X = 278/338 = 82%, Herd Y = 378/388 = 97%. Abbreviations: D, true disease status; T, test result.