Exploring Data Visually - Data Points: Visualization That Means Something - page 196

FIGURE 4-56 Box plot

The range in between the upper and lower quartiles is called the interquartile
range . The outer lines are the lower and upper fences, defined by subtracting
and adding 12 times the interquartile range from the lower and upper quartiles,
respectively. If the maximum and minimum values are within the upper and
lower fences, the outlines are only drawn to the extremes. Otherwise, dots are
used to represent any points that fall
outside the upper and lower fences
and are considered outliers.

That said, the terminology makes the
chart more confusing than it actu-
ally is. The main point: You can see a
general distribution with a box plot.
You can also use multiple box plots
to compare distributions, as shown
in Figure 4-57.

The histogram provides a more
detailed view, which you saw in
Figure 4-54. Bar height represents
the proportion of values within a
corresponding range, and when you
change bin sizes, you change how
much variability is visible. Figure 4-58
shows how the same height data can
be represented with different bins.

FIGURE 4-57 Multiple box plots for comparison