Suppose 1 in 25 adults is afflicted with a disease for which

Suppose 1 in 25 adults is afflicted with a disease for which a new diagnostic test has been developed. Given that an individual actually has the disease, a positive test result will occur with probability .99. Given that an individual does not have the disease, a negative test result will occur with probability .98.

Use a probability tree to answer the following questions.

 

Disease

No Disease

Probability of disease

0.04

0.96

Test Positive

0.99

0.02

Test Negative

0.01

0.98

 

Question 1. What is the probability of a positive test result?

Question 2. If a randomly selected adult is tested and the result is positive, what is the probability that the individual has the disease?

Question 3. If a randomly selected adult is tested and the result is negative, what is the probability that the individual does not have the disease?