Chapter 12 Quality Control 513
The Pareto Chart
After you have determined that your process is resulting in an unusual
number of problems, such as defects or accidents, the next natural step is
to determine what component in the process is causing the problems. This
investigation can be aided by a Pareto chart, which creates a bar chart of the
causes of the problem in order from most to least frequent so that you can
focus attention on the most important elements. The chart also includes the
cumulative percentage of these components so that you can determine what
combination of factors causes a certain percentage of the problems.
The Powder workbook contains data from a company that manufactures
baby powder. Part of the process involves a machine called a fi ller, which
pours the powder into bottles to a specifi ed limit. The quantity of powder
placed in the bottle varies because of uncontrolled variation, but the fi nal
weight of the bottle fi lled with powder cannot be less than 368.6 grams.
Any bottle weighing less than this amount is rejected and must be refi lled
manually (at a considerable cost in terms of time and labor). Bottles are
fi lled from a fi ller that has 24 valve heads so that 24 bottles can be fi lled at
one time. Sometimes a head is clogged with powder, and this causes the
bottles being fi lled on that head to receive less than the minimum amount
of powder. To gauge whether the machine is operating within limits, you
select random samples of 24 bottles (one from each head) at about one-
minute intervals over the nighttime shift at the factory. You’ve been asked
to examine the data and determine which part of the fi ller is most respon-
sible for defective fi lls.
To open the Powder workbook:
1 Open the Powder workbook from the Chapter12 data folder.
2 Save the workbook as Powder Pareto Chart. See Figure 12-18.
