Reconsider the previous exercise.
a. Determine a 90% confidence interval for the difference in proportions of undergraduates who held a credit card between the years 2001 and 2004.

b. Repeat (a) with a 95% confidence interval.
c. Repeat (a) with a 99% confidence interval.
d. Which (if any) of these intervals include the value 0? Summarize what you conclude from this.

Data from previous exercise

The Nellie Mae organization conducts an extensive annual study of credit card usage by college students. For their 2004 study, they analyzed credit bureau data for a random sample of 1,413 undergraduate students between the ages of 18 and 24. Th ey found that 76% of the students sampled held a credit card. Three years earlier they had found that 83% of undergraduates sampled held a credit card. (Assume that the sample size was similar in 2001.)