Question

2. An oxygen tension (arterial PO2) <90 mm Hg is one of the important criteria used in diagnosing this condition. Suppose that the sensitivity of this test is 95%, the specificity is 75% and the estimated prevalence of pulmonary embolism is 20%.

2a. What is the predictive value positive of the oxygen tension test?

2b. What is the meaning of the predictive value positive that you obtained in #2a.

Answer 1

	T+	T-	total
disease	0.19	0.01	0.2
no disease	0.2	0.6	0.8
total	0.39	0.61	1

a) predictive value positive of the oxygen tension test = 0.19/0.39 = 0.4872 or 48.72%

b)  predictive value positive means that if a persons is tested positive ,then there is 48.72% probability that he/she actually has disease(pulmonary embolism)