February 21, 2017

Homework Help: Math

Posted by Cami on Thursday, July 3, 2008 at 8:34pm.

You are a policeman on a case in which you believe there is a strong suspect. Based on your overall experience, your prior knowledge of this “person of interest,” and the evidence you’ve seen against him thus far, you believe that when he claims to be innocent there is a 80% chance that he is lying. He’s given a polygraph test which you believe to be “75% reliable [1] .” The results of the polygraph test indicate, to your surprise, that he is telling the truth! Given this new information, what should you say is the probability that he is still lying?

[1] You can take this to mean that when the subject is really telling the truth there is a 75% chance that he will pass the polygraph, and when he is lying there is a 75% chance that he will fail.

Choose one answer.
a. 25% or less
b. between 25% and 50%
c. exactly 50%.
d. between 50% and 80%
e. 80% or higher

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