8.14 In 1991 the average interest rate charged by Canadian credit card issuers was 18.8 percent. Since that time, there has been a proliferation of new credit cards affi liated with retail stores, oil companies, alumni associations, and so on. A fi nancial offi cer wants to study whether the increased competition in the credit card business has reduced interest rates. To do this, the offi cer will test a hypothesis about the current mean interest rate, m, charged by Canadian credit card issuers. To perform the hypothesis test, the offi cer randomly selects n 5 15 credit cards and obtains the following interest rates (arranged in increasing order): 14.0, 14.6, 15.3, 15.6, 15.8, 16.4, 16.6, 17.0, 17.3, 17.6, 17.8, 18.1, 18.4, 18.7, and 19.2. Is there a statistically signifi cant difference between present interest rates and historical rates? Present a standardized effect size estimate along with your hypothesis test.