CH10

10.11 An important feature of tablets is battery life, the num-ber of hours before the battery needs to be recharged. The file Tablets contains the battery life of 12 WiFi-only and 7 3G/4G/WiFi 9- through 12-inch tablets. (Data extracted from “Ratings and rec-ommendations: Tablets,” Consumer Reports, August 2013, p. 24.

)a. Assuming that the population variances from both types of tablets are equal, is there evidence of a difference in the mean battery life between the two types of tablets? 1Use a=0.05.2

b. Determine the p-value in (a) and interpret its meaning.

c. Assuming that the population variances from both types of tablets are equal, construct and interpret a 95% confidence interval estimate of the difference between the population mean battery life of the two types of tablets.

10.17 Brand valuations are critical to CEOs, financial and marketing executives, security analysts, institutional investors, and others who depend on well-researched, reliable information needed for assessments, and comparisons in decision making. Millward Brown Optimor has developed the BrandZ Top 100 Most Valuable Global Brands for WPP, the world’s largest com-munications services group. Unlike other studies, the BrandZ Top 100 Most Valuable Global Brands fuses consumer measures of brand equity with financial measures to place a financial value on brands. The file BrandZTechFin contains the brand values for two sectors in the BrandZ Top 100 Most Valuable Global Brands for 2014: the technology sector and the financial institutions sector. (Data extracted from bit.ly/18OL5Mu.)

a. Assuming that the population variances are equal, is there evi-dence of a difference between the technology sector and the financial institutions sector with respect to mean brand value? (Use a=.05.

b. Repeat (a), assuming that the population variances are not equal.

c. Compare the results of (a) and (b).

10.23 What motivates employees? The Great Place to Work Institute evaluated nonfinancial factors both globally and in the United States. (Data extracted from L. Petrecca, “Tech Companies Top List of ‘Great Workplaces,’” USA Today, October 31, 2011, p. 7B.) The results, which indicate the importance rating of each factor, are stored in Motivation .

a. At the 0.05 level of significance, is there evidence of a differ-ence in the mean rating between global and U.S. employees?

b. What assumption is necessary about the population distribution in order to perform this test?

c. Use a graphical method to evaluate the validity of the assump-tion in (b).

10.45 A problem with a telephone line that prevents a customer from receiving or making calls is upsetting to both the customer and the telecommunications company. The file Phone contains samples of 20 problems reported to two different offices of a tele-communications company and the time to clear these problems (in minutes) from the customers’ lines.

a. At the 0.05 level of significance, is there evidence of a differ-ence in the variability of the time to clear problems between the two central offices?

b. Determine the p-value in (a) and interpret its meaning.

c. What assumption do you need to make in (a) about the two populations in order to justify your use of the F test?

d. Based on the results of (a) and (b), which t test defined in Sec-tion 10.1 should you use to compare the mean time to clear problems in the two central offices?