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?