Vol. 6, No. 12
Marge Orrine, unfortunately, has lost her job at the butter factory since we visited her last month. It was not statistical incompetence that was her undoing, but instead it was the way she answered the phone (“Marge Orrine here”). Those who thought they were calling the Natural Butter Company were confused when they heard her voice, and since she had refused to use a different greeting, her departure seemed inevitable.
Ann Appladay, Marge’s replacement as quality manager, is fascinated with capability analysis, and is particularly enthusiastic about the Cpk statistic.
Ann rolls up her sleeves and launches an analysis of the weights of quarter-pound sticks of butter—the same problem that Marge had wrestled with for so many weeks. Ann notices that the process is in control, and remembers that this stability is a prerequisite to capability analysis. She also knows that the next step is a chi-squared [x2] test to assure that the data can be assumed to follow normal distribution.
Taking data from X-bar and R chart that she has made (25 samples of 5 each), Ann creates a histogram using CHARTrunner, since she knows that this software will perform chi-squared analysis, and takes the output to her boss, Rock deBote, for consideration. Noticing that the chi-squared value is 1.4, Ann points this out to him, adding that the standard deviation is nearly always one and a half times the chi-square.
Is Ann's explanation on solid ground?
2004 PQ Systems.
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