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

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.

Outliers

specifies how outliers are displayed. An outlier is a data point whose distance from the interquartile range is greater than 1.5 times the size of the interquartile range.

Select one of the following:

Ignore Outliers

excludes outliers from the plot. If you select this option, then outlier values are not represented in the plot.

Hide Outliers

includes the outliers within the whiskers. If you select this option, then outlier values are not represented differently from the other values in the plot.

Show Outliers

displays outliers separately from the whiskers. If there are a small number of outliers, then each outlier is displayed as a point. If there are a large number of outliers, then the range of outlier values is displayed as a bar.

Show averages

displays the mean value as a marker inside the box.

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 the Create new reference line button

, 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.