Citibank, which has a major credit card division, has instituted a promotion designed to encourage its customers to increase their current credit card usage. To test the effectiveness of this promotion, Citibank monitored the monthly credit card balances of 25 customers before and after the promotion was launched. The results can be found in the Excel file Citibank 1.xlsx.
a. Using α = 0.05, perform a hypothesis test to determine if the average credit card balance was higher after the promotion than before the promotion.
b. Construct a 90% confidence interval to estimate the average difference in a customer’s credit card balance before and after the promotion.
c. Verify your results using Excel or PHStat.
d. Identify the p value and interpret the result.
e. What assumptions need to be made in order to perform this procedure?