•Now suppose we don't know the probability of a stiff
neck, but we do know:
–the probability of whiplash P(W) = (1/1000)
–the probability of a stiff neck given whiplash P(S|W) = 0.8
•What is the relative likelihood of meningitis and
whiplash given a stiff neck?
•Write Bayes' Rule for each and write P(M|S)/P(W|S)
•P(M|S)/P(W|S) = (P(S|M)P(M)/P(S)) / (P(S|W)P(W)/P(S))
• = (P(S|M) P(M))/(P(S|W) P(W))
• = (0.5*(1/50000))/(0.8*(1/1000))
• = .00001 / .0008 = 1/80
