Question

In a certain population, the sensitivity of a diagnostic test is 0.80, and the specificity is 0.90.

The prevalence of the disease in the population is 0.10. Use this information to answer Ques-

tions 11 to 13.

11. What is the probability of testing negative?

(a) 0.17

(b) 0.20

(c) 0.47

(d)

•

0.83

12. Among those who have the disease of interest, what is the probability that they test

negative?

(a) 0.10

(b)

•

0.20

(c) 0.47

(d) 0.83

13. Among those who test positive, what is the probability that they have the disease?

(a) 0.10

(b) 0.20

(c)

•

0.47

(d) 0.8

Answer 1

from above:

	have	not have	total
positve	0.08	0.09	0.17
negative	0.02	0.81	0.83
total	0.1	0.9	1

11)  probability of testing negative =0.1*(1-0.8)+(1-0.1)*0.9 =0.83

12) P(negative|disease) =1-0.8 =0.2

13) P(have disease given tested positive) =0.1*0.8/(0.1*0.8+0.9*0.1)=0.08/0.17 =0.47