Spending on credit cards decreases after the Christmas spending season (as measured by amount charged on a credit card in December). The data set on the DVD with the same name as this exercise contains the monthly credit card charges of a random sample of 99 cardholders.

a) Build a regression model to predict January spending from December’s spending.

b) How much, on average, will cardholders who charged $ 2000 in December charge in January?

c) Give a 95% confidence interval for the average January charges of cardholders who charged $ 2000 in December.

d) From part c, give a 95% confidence interval for the average decrease in the charges of cardholders who charged $ 2000 in December.

e) What reservations, if any, do you have about the confidence intervals you made in parts c and d?