Working with Box Plots
About Box Plots
A box plot displays
the distribution of data values by using a rectangular box and lines
called “whiskers.”
Parts of a Box Plot shows a diagram of a box plot. The bottom and top edges
of the box indicate the interquartile range (IQR). That is, the range
of values that are between the first and third quartiles (the 25th
and 75th percentiles). The marker inside the box indicates the mean
value. The line inside the box indicates the median value.
You can enable outliers,
which are data points whose distances from the interquartile range
are greater than 1.5 times the size of the interquartile range.
The whiskers (lines
protruding from the box) indicate the range of values that are outside
of the interquartile range. If you do not enable outliers, then the
whiskers extend to the maximum and minimum values in the plot. If
you enable outliers, then the whiskers indicate the range of values
that are outside of the interquartile range, but are close enough
not to be considered outliers.
If there are a large
number of outliers, then the range of outlier values is represented
by a bar. The data tip for the bar displays additional information
about the outliers. To explore the outliers, double-click on the outlier
bar to view the values as a new histogram visualization.
Data Roles for a Box Plot
The basic data roles
for a box plot are categories and measures. You can assign one category
only, and the category values are plotted on the category axis. You
can assign many measures, and the measure values are plotted on the
response axis. At least one measure is required.
In addition to the basic
data roles, you can assign these roles:
Lattice columns
creates a lattice of
charts with a column for each value of the category data item that
you assign.
Lattice rows
creates a lattice of
charts with a row for each value of the category data item that you
assign.
Specify Properties for a Box Plot
On the Properties tab,
you can specify the following options:
Name
specifies the name
of the visualization.
Title
specifies the title
that appears above the graph.
Note: The Title option
is disabled if you select Generate graph title.
Generate graph title
specifies that the
graph title is generated automatically based on the data items in
the visualization.
Show grid lines
displays grid lines
for each tick on the response axis.
Box direction
specifies whether the
boxes are vertical or horizontal.
Overview
specifies whether the
chart overview is enabled.
Measure layout
specifies whether the
measures share a single response axis (Shared axis)
or have separate response axes for each measure (Separate
axes).
Note: The Measure layout option
is disabled if your visualization contains exactly one measure.
Show averages
displays the mean value
as a marker inside the box.
Show outliers
shows outliers outside
of the whiskers. Outliers are data points whose distances from the
interquartile range are greater than 1.5 times the size of the interquartile
range.
Rotate axis labels
displays the category
labels at an angle.
Note: The Rotate axis
labels option has no effect if the box plot contains
no categories.
Reference Lines
adds reference lines
to the visualization. To create a reference line, click 
, and then specify the parameters for the line in
the New Reference Line window.
, and then specify the parameters for the line in
the New Reference Line window.
The name of each reference
line appears below the Reference Lines option.
You can edit or delete your reference lines by using the icons next
to each name.
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