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11
Simple Boxplot
PURPOSE OF GR APHS YOU ARE ABOUT TO BUILD
•• To compare the variability of a continuous variable categorized by a discrete variable
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11.1 introduction to the Simple Boxplot
First, we advise you not to be misled by what we consider to be a confusing
name especially when this graph is compared with the 1-D boxplot described
in the previous chapter. The simple boxplot discussed in this chapter is not
as “simple” as the 1-D boxplot. The simple boxplot is not more difficult to
build; however, it does convey considerably more information making it
much more complex than the 1-D boxplot.
The simple boxplot displays the same five statistics as you did in the
previous chapter (minimum, first quartile, median value, third quartile, and
maximum value). Recall that these statistics were calculated for a single con-
tinuous variable. In that chapter, we used a single continuous variable, but
the simple boxplot takes it a step beyond. The simple boxplot displays the
same five statistics but separates the continuous variable into the several
categories of a discrete variable. For an example of the simple boxplot, look
at Figure 11.1 that uses data describing 1,050 students in terms of test perfor-
mance (score on final exam) and hour of their class.
