Question

Juliet is being tested for a contagious disease. The test is 99% accurate and in actuality 0.1% of the population has the disease. Juliet still thinks she has the disease even though she tested negative. Is she worrying too much? Explain.

A She is worrying too much as the test is 99% accurate.
B She should be worried as there is a 9% probability that she is sick.
C She should be worried as there is still a 1% chance she has the disease.
D She is worrying too much as the probability that she is sick given she tested negative is 0.0001

CORRECT ANSWER IS D

Answer 1

D

Explanation:

You are looking for a conditional probability. P(has the disease given that you tested negative). This probability is

1

9891

= 0.0001. Which means that the likelihood she has the disease is very small. Therefore, She is worrying too much as the probability that she is sick given she tested negative is 0.0001

Answer 2

I agree with the answer D because the negative tests of .0001 can still give a worry to the patient even if the probability is less.