SAS Macro Programs: boxplot
$Version: 2.1 (09 Jan 2005)
The BOXPLOT macro draws side-by-side boxplots for the groups
defined by one or more grouping (CLASS) variables in a data set.
The boxplots may be formatted horizontally or vertically,
they may be shown with "notches", indicating approximate
95% confidence intervals for difference in medians,
and the groups may be ordered in a variety of ways.
- Name of the input data set.
- Grouping variable(s). The CLASS= variables
may be character or numeric. If the CLASS= variable
is a character variable, or there is more than one
CLASS= variable, the macro automatically constructs
a SAS format to label the group.
- The name of the response variable to be plotted.
The VAR= variable is plotted on the ordinate when ORIENT=V and on
the abscissa when ORIENT=H.
- A character variable to identify each
observation. If an ID= variable is specified,
outside variables are labelled on the graph,
using the first 8 characters of the value of
the ID variable (to reduce overplotting).
Otherwise, outside points are not labelled.
- Specifies a variable or statistic keyword used to
order the levels of the CLASS= variables along the class axis.
If SORTBY= is not specified, the classes are ordered along the
axis in sorted order (using the format specified by CLASSFMT=
if that has been used).
Otherwise, you can specify the name of a variable in the dataset,
or one of the statistics,
_MEAN_, _MEDIAN_, N (no underscores), _Q1_, or _Q3_
and the classes will be ordered on the axis according to the
values of that statistic for each group.
- Box width as proportion of the maximum.
The default, width=.5, means that the maximum
box width is half the spacing between boxes.
- Specifies whether or not to draw notched
boxes. 1=draw notched boxes; 0=do not.
- Color for box fill. If specified, the area
inside the box outline is filled using a solid pattern and the
CFILL color. A light grey, e.g., CFILL=GRAYD0 is often pleasing.
- Color for notch fill. If specified, the area
between the upper/lower notches is filled using a solid pattern and the
CNOTCH color. This is often an alternative to drawing explicit
- Line style for box outline
- Box orientation: V gives vertical boxes, H gives
horizontal boxes. If the labels for the CLASS= variables are longish,
horizontal boxes are preferred, since the labels will appear on the
- Specifies the line style used to connect
medians of adjacent groups. If CONNECT=0, the
medians of adjacent groups are not to be
- For a notched boxplot, the parameter F
determines the notch depth, from the center of
the box as a fraction of the halfwidth of each
box. F must be between 0 and 1; the larger the
value, the less deep is the notch.
- Box width proportionality factor. The
default, FN=1 means all boxes are the same
width. If you specify FN=sqrt(n), the boxes
width will be proportional to the square root
of the sample size of each group. Other
functions of n are possible as well.
- The name of a format for the VAR= analysis
- The name of a format for the class
variable(s). If the CLASS variable is a character variable, or
there are two or more CLASS variables, the program maps the sorted
values of the class variable(s) into the integers 1, 2, ...
levels, where levels is the number of distinct values
of the class variable(s). A format provided for CLASSFMT should
therefore provide labels corresponding to the numbers 1, 2, ...
- Label for the analysis variable. If not
specifed, the analysis axis is labelled with the
- Label for the class variable(s) used to
label the axis.
- Tick marks, and range for the horizontal axis, in the
form XORDER = low TO high BY
tick. With ORIENT=V, the horizontal axis pertains to the
CLASS= variable(s); with ORIENT=H, the horizontal axis pertains to
the VAR= analysis variable.
When there are very few (3 or less) levels of the CLASS= variable, SAS/GRAPH
often has problems dealing with the annotation information and labels.
Setting XORDER= (or YORDER=, with ORIENT=H) to include an extra
value at both ends of the range usually helps cure this problem.
For example, if there are only two groups, with class values 1 and 2,
set XORDER=0 to 3 by 1.
- Tick marks, and range for ordinate, in the
form YORDER = low TO high BY
- The name of an (optional) additional
ANNOTATE data set to be used in drawing the
plot. This requires some knowledge of the
contents of the ANNOTATE data set, which you can
see by specifying PRINT=ANNO in a previous call.
- Printed output: any one or more of
ANNO, OUTSIDE, STATS.
- Name of the output data set containing
statistics used in drawing the boxplot. There
is one observation for each group. The
variables are N, _MEAN_, _MEDIAN_, _Q1_, _Q3_, _IQR_,
LO_NOTCH, HI_NOTCH, LO_WHISK, HI_WHISK.
- The name assigned to the graph in the
If there are many groups and/or the formatted labels of group names
are long, you may need to increase the HPOS= option to allow a
sufficient number of character positions for the labels.
The font face and size used for labels is controlled by the
global graphics options FTEXT and HTEXT.
The example below plots data for 6 groups in a 2 x 3 design,
classified by factors A and B. No explicit notches are drawn,
but the region between the notches is filled in red.
title h=1.5 'Notched Boxplot: 2 x 3 design';
class= A B,
notch=0, /* 1=do notched boxplots */
classfmt=ab., /* Format for class variables */