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222 Part IV: Quality Assurance
Bar Chart
Bar charts are commonly used to study one or more populations when they are
classified into various categories, for example, by sector, by region, or over different
time periods, and so on. For example, we may want or need to know more
about the sales of our company by sector, by region, or over different time periods.
Different sectors, different regions, or different time periods are usually labeled as
different categories. A bar chart is constructed by creating categories that are represented
by intervals of equal length on a horizontal axis. Within each category we
then indicate observations as a frequency of the corresponding category, which is
represented by a bar of length proportional to the frequency. We illustrate the construction
of bar charts in Examples 18.20 and 18.21.
Pareto Chart
The Pareto chart is a very useful tool to use whenever one wants to learn more
about attribute data quickly and visually. The Pareto chart, named after Vilfredo
EXAMPLE 18.20
The following data give the annual revenues (in millions of dollars) of a company over a
period of five years (1998–2003).
Construct a bar chart for these data.
78 92 95 94 102
Part IV.A.4
Solution:
Following the above discussion we construct the bar chart shown in Figure 18.10.
100
80
60
40
20
0
1998 1999 2000 2001 2002
Figure 18.10 Bar chart for annual revenues of a company over a five-year period.