Vol. 11, No. 8
August 2009
PQ Systems
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Quality Quiz from Professor Cleary

Anna Gramm is learning to make charts for Deer Dairy Farms, a small firm that produces ice cream. In evaluating the quality of the finished product, the company is insistent on consistency among all the ice cream that is shipped. For chocolate-chip-cookie-dough ice cream, for example, inspectors examine content for the number of chocolate chips and the amount of cookie dough in sample containers of the product. In addition, inspectors must evaluate creaminess factors and melt temperature for each sampled container, and must examine the container label to be sure that it accurately indicates contents, that it is applied straight, and that the printing is correct. This proofreading task was added to their task list after a shipment went out that proclaimed the name of the dairy as “Dear Diary,” so the firm is sensitive about its image.

Anna understands attributes charts, so she decides to create a p-chart to reflect the proportion of nonconforming items in each day’s shipments, based on a batch of 100 cartons of ice cream. She explains p-charts to her inspectors and sends them on their way.

Unfortunately, they come back, puzzled by the data that they are receiving. “We know how many are bad, but we don’t know why,” they explain. “We are rejecting lots of ice cream, which our employees are taking home to their families. These customers never complain about the quality, so we don’t learn anything by rejecting the ice cream samples.” They wondered how their p-charts could help the company improve the quality of its ice cream and reduce the rejection rate.

Anna assures them that after enough data has been collected, it will be analyzed and the answer will be useful with respect to improving quality. But as she says this, she’s not so sure that this is the case. How can Anna Gramm improve the data analysis so that it will lead to better quality?

a) Create larger sample sizes.

b) Sample more frequently.

c) Use a u-chart instead of p-chart.


Click here for a more complete video explanation

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