Random samples of students at 111 four-year colleges were interviewed several times since 1999. Of the students who reported drinking alcohol, the percentage who reported bingeing at least three times within the past two weeks was 41.5% of 337 students in 1999 and 21 % of 841 students in 2004. a. Estimate the difference between the proportions in 2004 and 1999, and interpret. b. Find the standard error for this difference. Interpret it. c. Define the two relevant population parameters to compare in the context of this exercise. d. Construct and interpret a 95% confidence interval to estimate the true difference. e. State the assumptions for the confidence interval in part d to be valid.