Question

2.24 Exit poll: Edison Research gathered exit poll results from several sources for the Wisconsin recall election of Scott Walker. They found that 57% of the respondents voted in favor of Scott Walker. Additionally, they estimated that of those who did vote in favor for Scott Walker, 33% had a college degree, while 45% of those who voted against Scott Walker had a college degree. Suppose we randomly sampled a person who participated in the exit poll and found that he had a college degree. What is the probability that he voted in favor of Scott Walker? (please round to 4 decimal places)

Answer 1

Answer:

0.4929 = 49.29% probability that he voted in favor of Scott Walker

Step-by-step explanation:

Bayes Theorem:

Two events, A and B.

$P(B|A) = \frac{P(B)*P(A|B)}{P(A)}$

In which P(B|A) is the probability of B happening when A has happened and P(A|B) is the probability of A happening when B has happened.

In this question:

Event A: Having a college degree.

Event B: Voting for Scott Walker.

They found that 57% of the respondents voted in favor of Scott Walker.

This means that $P(B) = 0.57$

Additionally, they estimated that of those who did vote in favor for Scott Walker, 33% had a college degree

This means that $P(A|B) = 0.33$

Probability of having a college degree.

33% of those who voted for Scott Walker(57%).

45% of those who voted against Scott Walker(100 - 57 = 43%). So

$P(A) = 0.33*0.57 + 0.45*0.43 = 0.3816$

What is the probability that he voted in favor of Scott Walker?

$P(B|A) = \frac{0.57*0.33}{0.3816} = 0.4929$

0.4929 = 49.29% probability that he voted in favor of Scott Walker