September 2001

Vol. 3, No. 9

Quality Quiz

Here's September's question from Professor Cleary. After you have read the question, click on the response that you think is correct. If you answer correctly, you can register to win a free copy of Quality Gamebox.

Dick Moby, quality assurance czar for a plastics extrusion company somewhere in the Midwest, is serious about control charts. He sees data analysis and process control as ways not only to assure high quality products for his firm, but also to enhance his own career. He personally instructs each new employee in his department, giving them a solid foundation in the fundamentals of SPC. He has given the same attention to Wanda Ring, who also aspires to advancement in the organization, and has emphasized the importance of keeping all process data points between the upper and lower control charts. 

Wanda Ring is assigned to monitor a series of machines that extrude raw materials used for manufacturing parts for toys. One of these machines, she believes, is not operating with the same consistency that others on the line demonstrate. Since she had some fleeting experience as an operator prior to being hired by Dick Moby, she feels confident that by adjusting the operation of the machine she can reduce the variability of the process. The operator advises her not to tamper with the machine, since this can contribute to variability in the process, but she says that she knows what she's doing.

Wanda is using an individuals moving average chart. She decides to adopt a decision rule: if a point falls above X-bar, she will adjust the operation of the machine downward to compensate for the distance between the data point and X-bar. If a data point falls below X-bar, on the other hand, she would adjust the operation upward to compensate.

If Wanda follows this decision rule, which of the following will be true?

A) Variability of the process will decrease by 50 percent;

B) Variability of the process will increase by 100 percent;

C) Variability will remain the same;

D) Variability will increase by 25 percent.

Click on the correct answer, and link to the solution.


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