November  2002

Vol. 4, No. 11

Quality Quiz

Mark Miwerds, owner of a chain of three fabric stores called Sew n Sew, is convinced that if he could just persuade employees of the value of using statistics in quality improvement, his customers would be happier and his profits higher. He imagines being able to expand Sew n Sew's reach to every city in the state, then going public in order to channel investments into further expansion efforts. 'Just think, ' he says to a co-worker, 'we could be in a position of winning the first Baldrige Award for fabric retailing! ' The co-worker, more skeptical of the possibilities, advises him to start with the home store, and see how the whole thing goes from there. 
After a great deal of thought, Mark Miwerds has decided that he can teach employees about collecting data and analyzing that data with control charts. Accordingly, they have learned about check sheets and run charts as a way of recording day-to-day data related to store sales, yards of fabric cut, sundries sold, and other critical information for the store. Since they've gathered data on sticky notes rather than just writing figures in a ledger, they're excited about the next steps.
What comes next is the onerous task of calculating the mean and standard deviation for data. Mark writes the formula on the board:


Mark is highly confident about simple statistics, as long as everything fits the formula and no one asks questions.  In this case, however, someone does ask a question. 'Why are you dividing the squared deviations from the mean by n 1 instead of n? '
Mark Miwerds was afraid of this. Some smart aleck who remembered basic statistics from the classroom. 'Well, we'll see how smart you really are, ' Mark mumbled to himself, and then responded by bluffing with what he remembered (and that wasn't much) about degrees of freedom. 'You divide by n 1 to compensate for the fact that you have taken the square root of the deviation, '  he announced confidently.
Was his shot-in-the-dark answer a correct one, by any chance?
A. Yes
B. No

Copyright 2002 PQ Systems.

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