A political candidate feels that she performed particularly well in the most recent debate against her opponent. Her campaign manager polled a random sample of 400 likely voters before the debate and a random sample of 500 likely voters after the debate. The 95% confidence interval for the true difference (post-debate minus pre-debate) in proportions of likely voters who would vote for this candidate was (-0.014, 0.064). What was the difference (pre-debate minus post-debate) in the sample proportions of likely voters who said they will vote for this candidate?
a. 0.064 + (-0.014) / 2 = 0.025
b. 0.064 - (-0.014) / 2 = 0.039
c. 0.064 + (-0.014) = 0.050
d. 0.064 - (-0.014) = 0.078