Predictive Values

• Positive Predictive Value (PPV)
• Negative Predictive Value (NPV)

		Disease						Disease
		Present	Absent	Total				Present	Absent	Total
Test	Pos					Test	Pos	a: (True + ve)	b: (False + ve)	a + b
	Neg						Neg	c: (False - ve)	d: (False - ve)	c + d
	Total						Total	a + c	b + d	n
PPV: The proportion of those testing positive who actually have disease. (PPV = a/(a + b)).
NPV: The proportion of those testing negative who actually do not have disease. (NPV = d/(c + d)).