September 2003  

Vol. 5, No. 9


Quality Quiz

Dr. Barbara SeVille has learned about the use of control charts, standard deviations, and histograms from a workshop she attended at a national conference of the Institute for Healthcare Improvement. She has seen for herself how these concepts help hospitals and other health care institutions to organize and analyze their data, and is determined to use statistical process control to improve measures of quality at St. Maybe Hospital. In this effort, she engages her staff in a training effort to assure that all members of her department will be on the same page when it comes to statistics.

And speaking of pages, she keeps at least a page ahead of the group that she is training in these methods. So while everyone else may be on the same page, Dr. SeVille stays up late at night to assure herself that she knows more than those whom she is training.

After she has demonstrated the formula for calculating standard deviation and shown her trainees how control charts will help them understand processes, she introduces CHARTrunner, a software program that creates charts from data in established databases and spreadsheets such as Excel. "This will make your life easier," she promises, but as it turns out, it may be on the verge of making her life harder. Collette D'Bills, one of her department managers, comes across the coefficient of variation as she explores the printout of her charted data. She asks Dr. Barbara SeVille to explain.

Although this chapter on coefficient of variation is not one that Barbara has studied yet, she feels compelled to respond, especially since the entire class is looking expectantly at her and waiting for her answer. "That's really the sum of the log of the standard deviation," she mumbles. Although no one understands what she means, trainees nod their heads and take notes.

Was this the right definition for coefficient of variation? If so, was Dr. Barbara SeVille's response an inspired guess or an intuitive speculation? Is it important to understand this concept? Stay tuned to learn more about this exciting turn of events in the life of Dr. Barbara SeVille, statistician.

We have a pretty good sense that Barbara SeVille doesn't know what she's talking about. So, what is the coefficient of variation, anyway?
Select one of the following responses:

A) the capability of a process;

B) whether a process is in or out of control;

C) the peakedness of a distribution;

D) the ratio of the standard deviation to the mean in a data set.


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