Statistics for quantity: Control and Capability
• Quality is a broad concept. Often it refers to a degree or grade of excellence. For example, you
may feel that a restaurant serving ﬁlet mignon is a higher-quality establishment than a fast-food
outlet that serves hamburgers.
• You may also consider a name-brand sweater of higher quality than one sold at a discount store.
In this chapter, we consider a narrower concept of quality: consistently meeting standards
appropriate for a speciﬁc product or service.
• The fast-food outlet, for example, may serve high-quality hamburgers.
• The hamburgers are freshly grilled, are served at the right temperature, and are the same every
time you visit. The discount store sweaters may be high quality because they are consistently
free of defects and the tight knit helps them keep their shape wash after wash. Statistically
minded management can assess quality through sampling.
• For example, the fast-food outlet could sample hamburgers and measure the time from order to
being served, the temperature of the burgers, and their tenderness.
• This chapter discusses the methods used to monitor the quality of a product or service and
effectively detect changes in the process that may affect its quality.
Membership renewal process
• Use of data to assess quality Organizations are (or ought to be) concerned about the quality of
the products and services they offer.
• What they don’t know about quality can hurt them: rather than make complaints that an alert
organization could use as warnings, customers often simply leave when they feel they are
receiving poor quality.
• A key to maintaining and improving quality is systematic use of data in place of intuition or
anecdotes. Here are two examples.
• Sometimes data that are routinely produced make a quality problem obvious.
• The internal ﬁnancial statements of a professional society showed that hiring temporary
employees to enter membership data was causing expenditures above budgeted levels each
year during the several months when member