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Chapter 18: A. Basic Statistics and Applications 215
2. The interquartile range is potentially a more meaningful measure of
dispersion than range, since it is not affected by the extreme values that
may be present in the data. By trimming 25 percent of the data from the
bottom and 25 percent from the top we eliminate the extreme values that
may be present in the data set. Very often, interquartile range is used as
a measure for comparing two or more data sets from similar studies.
4. GRAPHICAL DISPLAYS
Define, interpret, and distinguish between
graphical displays, such as histograms,
scatter diagrams, tally sheets, bar charts,
etc., and apply them in various situations.
(Application)
Body of Knowledge IV.A.4
In this section we start our discussion of graphical displays by considering an
important tool called the frequency distribution table. The frequency distribution
table constitutes the first step toward displaying data graphically.
Frequency Distribution Table
Graphical methods allow us to visually observe characteristics of the data, as
well as to summarize pertinent information contained in the data. The frequency
distribution table is a powerful tool that helps summarize both quantitative and
qualitative data, enabling us to prepare the additional types of graphics that are
discussed in this section.
Qualitative Data
A frequency distribution table for qualitative data consists of two or more categories
along with the data points that belong to each category. The number of data
points that belong to any particular category is called the frequency of that category.
For illustration let us consider the following example.
Part IV.A.4
EXAMPLE 18.15
Consider a random sample of 110 small to mid-size companies located in the Midwestern
region of the United States, and classify them according to their annual revenues (in
millions of dollars).
Continued