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Chapter 4 • Business Reporting, Visual Analytics, and Business Performance Management 181

BAR ChARt Bar charts are among the most basic visuals used for data representation.
Bar charts are effective when you have nominal data or numerical data that splits nicely
into different categories so you can quickly see comparative results and trends within
your data. Bar charts are often used to compare data across multiple categories such as
percent advertising spending by departments or by product categories. Bar charts can be
vertically or horizontally oriented. They can also be stacked on top of each other to show
multiple dimensions in a single chart.

pie ChARt Pie charts are visually appealing, as the name implies, pie-looking charts.
Because they are so visually attractive, they are often incorrectly used. Pie charts should
only be used to illustrate relative proportions of a specific measure. For instance, they
can be used to show relative percentage of advertising budget spent on different product
lines or they can show relative proportions of majors declared by college students in their
sophomore year. If the number of categories to show are more than just a few (say, more
than 4), one should seriously consider using a bar chart instead of a pie chart.

sCAtteR plot Scatter plots are often used to explore relationships between two or
three variables (in 2D or 2D visuals). Since they are visual exploration tools, having
more than three variables, translating into more than three dimensions, is not easily
achievable. Scatter plots are an effective way to explore the existence of trends, concen-
trations, and outliers. For instance, in a two-variable (two-axis) graph, a scatter plot can
be used to illustrate the co-relationship between age and weight of heart disease patients
or it can illustrate the relationship between number of customer care representatives and
number of open customer service claims. Often, a trend line is superimposed on a two-
dimensional scatter plot to illustrate the nature of the relationship.

BuBBle ChARt Bubble charts are often enhanced versions of scatter plots. The bubble
chart is not a new visualization type; instead, it should be viewed as a technique to
enrich data illustrated in scatter plots (or even geographic maps). By varying the size and/
or color of the circles, one can add additional data dimensions, offering more enriched
meaning about the data. For instance, it can be used to show a competitive view of
college-level class attendance by major and by time of the day or it can be used to show
profit margin by product type and by geographic region.

specialized Charts and graphs
The graphs and charts that we review in this section are either derived from the basic
charts as special cases or they are relatively new and specific to a problem type and/or
an application area.

histogRAM Graphically speaking, a histogram looks just like a bar chart. The difference
between histograms and generic bar charts is the information that is portrayed in them.
Histograms are used to show the frequency distribution of a variable, or several variables.
In a histogram, the x-axis is often used to show the categories or ranges, and the y-axis
is used to show the measures/values/frequencies. Histograms show the distributional
shape of the data. That way, one can visually examine if the data is distributed normally,
exponentially, and so on. For instance, one can use a histogram to illustrate the exam
performance of a class, where distribution of the grades as well as comparative analysis
of individual results can be shown; or one can use a histogram to show age distribution
of their customer base.

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