Question

An article in the Journal of the American Medical Association in 1997 reported that, when people go to their doctor's office with a sore throat and think they might have strep throat, 30% actually have strep throat.  It noted that a current test for strep throat was 80% accurate if you have strep throat and 90% accurate if you do not.  The following conditional probability tree diagram shows a person who may or may not have strep throat (B) and his/her test results (A).  A is a positive and not A is a negative test result.  What is the probability that a person will test positive?  (write your answers in decimal form)What is P(not A) = What is the probability of a false negative?

Answer 1

B is may or may not have step throat.

A is the result of the test.

The probability that a person will test positive is the addition of the test being positive either when it may or nay not have the desease, Then:

`0.24+0.07=0.31`

The probability of not A is:

`0.06+0.63=0.69`

The probability of a false negative is the complement of the above, then:

`1-0.69=0.31`