Required Tasks:
1. Review results from Case 10.1.
2. Conduct the appropriate hypothesis test to determine whether the two suppliers have equal standard deviations. (Test using a significance level equal to 0.05.)
3. Prepare a short report that ties together the results from Cases 10.1 and 11.1 to present to Cregg along with a conclusion as to whether the new supplier seems viable based on rivet diameters.
Cregg Hart is manufacturing manager for Motive Power Company, a locomotive engine and rail car manufacturer (see Case 10.1). The company has been very successful in recent years, and in July 2006 signed two major contracts totaling nearly $200 million. A key to the company’s success has been its focus on quality. Customers from around the world have been very pleased with the attention to detail put forth by Motive Power.
In Case 10.1, Sheryl Carleson came to Cregg with a new supplier of rivets that would provide a substantial price advantage for Motive Power over the current supplier. Cregg asked Sheryl to conduct a study in which samples of rivets were selected from both suppliers. (Data are in the file called Motive Power.) In Case 10.1, the focus was on the mean diameter and a test to determine whether the population means were the same for the two suppliers. However, Cregg reminds Sheryl that not only is the mean diameter important, so too is the variation in diameter. Too much variation in rivet diameter adversely affects quality. Cregg showed Sheryl the following table to emphasize what he meant:

As Sheryl examined this example that Cregg had prepared, she was quickly convinced that looking at the mean diameters would not be enough to fully compare the rivet suppliers. She told Cregg that she would also ask her intern to perform the following tasks.