Help with Probabilities Homework

aaron.johnson3

New member
Joined
Oct 25, 2013
Messages
1
1. In order to help with a possible zombie outbreak, the CDC1
has developed three tests to help
determine if you are a zombie. Test #1 is inexpensive, but has a 20% false-positive rate. Test
#2 is a little pricey, but has a 10% false-positive rate. And Test #3, while very expensive, has
only a 5% false-positive rate. All three tests have a 10% false-negative rate. Luckily, for
now, the chance you are a zombie is only 1%. Answer the following questions and show your
work.
a. Suspecting you might be a zombie, you go to the hospital, and they perform Test #1
on you. The test comes back positive. What is the probability you are a zombie based
on the results of this test?
b. Noting the high false-positive rate of Test #1, the hospital recommends performing
Test #2. Luckily, the test is covered by your new insurance policy, so you agree.
Unfortunately, the test comes back positive. Based on the positive results of Test #1
and Test #2, what is the probability you are a zombie?
c. Convinced you are not a zombie, you insist on Test #3. Unfortunately, this test also
returns a positive result. As the Zombie Extraction Team approaches in their Hazmat
suits, you exclaim “Wait! There is still a chance I’m not a zombie!” What is the
probability you are not a zombie, given that all three tests returned a positive result?
 
1. In order to help with a possible zombie outbreak, the CDC1
has developed three tests to help
determine if you are a zombie. Test #1 is inexpensive, but has a 20% false-positive rate. Test
#2 is a little pricey, but has a 10% false-positive rate. And Test #3, while very expensive, has
only a 5% false-positive rate. All three tests have a 10% false-negative rate. Luckily, for
now, the chance you are a zombie is only 1%. Answer the following questions and show your
work.
a. Suspecting you might be a zombie, you go to the hospital, and they perform Test #1
on you. The test comes back positive. What is the probability you are a zombie based
on the results of this test?
b. Noting the high false-positive rate of Test #1, the hospital recommends performing
Test #2. Luckily, the test is covered by your new insurance policy, so you agree.
Unfortunately, the test comes back positive. Based on the positive results of Test #1
and Test #2, what is the probability you are a zombie?
c. Convinced you are not a zombie, you insist on Test #3. Unfortunately, this test also
returns a positive result. As the Zombie Extraction Team approaches in their Hazmat
suits, you exclaim “Wait! There is still a chance I’m not a zombie!” What is the
probability you are not a zombie, given that all three tests returned a positive result?
I don't see your work, so I can't comment on it.

Have you been studying Bayes's Theorem? What other tools do you have?

Your "prior" probability is 1%. How is that modified by the results of test 1?

Use that as your prior when test 2 is performed, etc.

Show us what you have done.
 
Top