Re: JNU Doubts

Posted by Amit Goyal on Apr 16, 2014; 8:07am
URL: http://discussion-forum.276.s1.nabble.com/JNU-Doubts-tp7586990p7587029.html

Let B be the event that there is a black dot in examinee's answer script and C be the event that the examinee cheat. We want to find the probability that the answer script came from a cheater given that his answer script has a black dot. That is, we wish to find
Pr(C|B) = Pr(B|C)Pr(C)/ [Pr(B|C)Pr(C)+Pr(B|C')Pr(C')]
We know Pr(B|C) = 1, Pr(C) = 0.05 and Pr(C') = 0.95
But we don't know Pr(B|C'). That is, the missing information is the probability of the event that the answer script has a black dot given that the script belongs to someone who did not cheat.