The Seitz Corporation, a QS 9000 certified organization based in Torrington,Connecticut, is a leading designer and manufacturer of thermoplastic motion control systems and components and an industry leader in plastics and gear trains. Founded in 1949 by the late Karl F. Seitz, the company began as a small tool-making business and grew slowly. In the late 1960s, the company expanded its services to include custom injection molding. As their customer base grew to include leading printer manufacturers, Seitz developed and patented a proprietary line of perforatedform handling tractors. Utilizing its injection-molding technology, the company engineered an all-plastic tractor called Data Motion, which replaced costly metal versions. By the late 1970s, business was booming, and Data Motion had become the worldwide industry leader.

Discussion

1. Seitz's list of several hundred business-to-business customers continues to grow. Managers would like to know whether the average dollar amount of sales per transaction per customer has changed from last year to this year. Suppose company accountants sampled 20 customers randomly from last year's records and determined that the mean sales per customer was $2,300, with a standard deviation of $500. They sampled 25 customers randomly from this year's files and determined that the mean sales per customer for this sample was $2,450, with a standard deviation of $540. Analyze these data and summarize your findings for managers. Explain how this information can be used by decision makers. Assume that sales per customer are normally distributed.

2. One common approach to measuring a company's quality is through the use of customer satisfaction surveys. Suppose in a random sample, Seitz's customers are asked whether the plastic tractor produced by Seitz has outstanding quality (Yes or No).Assume Seitz produces these tractors at two different plant locations and that the tractor customers can be divided according to where their tractors were manufactured. Suppose a random sample of 45 customers who bought tractors made at plant 1 results in 18 saying the tractors have excellent quality and a random sample of 51 customers who bought tractors made at plant 2 results in 12 saying the tractors have excellent quality. Use a confidence interval to express the estimated difference in population proportions of excellent ratings between the two groups of customers. Does it seem to matter which plant produces the tractors in terms of the quality rating received from customers? What would you report from these data?

3. Suppose the customer satisfaction survey included a question on the overall quality of Seitz measured on a scale from 0 to 10 where higher numbers indicate greater quality. Company managers monitor the figures from year to year to help determine whether Seitz is improving customers' perceptions of its quality. Suppose random samples of the responses from 2008 customers and 2009 customers are taken and analyzed on this question, and the following Minitab analysis of the data results. Help managers interpret this analysis so that comparisons can be made between 2008 and 2009. Discuss the samples, the statistics, and the conclusions.

4. Suppose Seitz produces pulleys that are specified to be 50 millimeters (mm) in diameter. A large batch of pulleys is made in week 1 and another is made in week 5. Quality control people want to determine whether there is a difference in the variance of the diameters of the two batches. Assume that a sample of six pulleys from the week 1 batch results in the following diameter measurements (in mm): 51, 50, 48, 50, 49, 51.Assume that a sample of seven pulleys from the week 5 batch results in the following diameter measurements (in mm): 50, 48, 48, 51, 52, 50, 52. Conduct a test to determine whether the variance in diameters differs between these two populations.Why would the quality control people be interested in such a test? What results of this test would you relate to them? What about the means of these two batches? Analyze these data in terms of the means and report on the results. Assume that pulley diameters are normally distributed in thepopulation.

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Two-Sample T-Test and CI: 2008, 2009 Two-sample T for 2008 vs 2009 NMean StDev SE Mean 75 6.466 0.352 0.041 93 6.604 0.398 0.041 2008 2009 Difference mu (2008)-mu (2009) Estimate for difference: -0.1376 95% CI for difference: (-0.2535, -0.0217) T-Test of difference0 (s not0) T-Value 2.34 P-Value = 0.020 DF = 166 Both use pooled StDev = 0.3782