Charge more, III In Exercises 10.41 and 10.42, you carried

Chapter 10, Problem 10.43

(choose chapter or problem)

Charge more, III In Exercises 10.41 and 10.42, you carried out the calculations for a test and confi dence interval based on a banks experiment in changing the rules for its credit cards. You ought to ask some questions about this study. (a) Th e distribution of the amount charged is skewed to the right, but outliers are prevented by the credit limit that the bank enforces on each card. Why can we use a test and confi dence interval based on a Normal sampling distribution for the sample mean x? (b) Th e banks experiment was not comparative. Th e increase in amount charged over last year may be explained by lurking variables rather than by the rule change. What are some plausible reasons why charges might go up? Outline the design of a comparative randomized experiment to answer the banks question.