Chapter 9.2, Problem 1AC

Too Long on the Telephone

A company collects data on the lengths of telephone calls made by employees in two different divisions. The sample mean and the sample standard deviation for the sales division are 10.26 and 8.56, respectively. The sample mean and sample standard deviation for the shipping and receiving division are 6.93 and 4.93, respectively. A hypothesis test was run, and the computer output follows.

Degrees of freedom = 56

Confidence interval limits = −0.18979, 6.84979

Test statistic t = 1.89566

Critical value t = −2.0037, 2.0037

P-value = 0.06317

Significance level = 0.05

1. Are the samples independent or dependent?

2. Which number from the output is compared to the significance level to check if the null hypothesis should be rejected?

3. Which number from the output gives the probability of a type I error that is calculated from the sample data?

4. Was a right-, left-, or two-tailed test done? Why?

5. What are your conclusions?

6. What would your conclusions be if the level of significance were initially set at 0.10?

See pages 544–545 for the answers.