VIOLIN PLOT

VIOLIN PLOT

Graphics Command

Generates a violin plot.

A violin plot is a combination of a box plot and a kernel density plot. Specifically, it starts with a box plot. It then adds a rotated kernel density plot to each side of the box plot.

Enter HELP BOX PLOT and HELP KERNEL DENSITY PLOT for details on the construction of box plots and kernel density plots, respectively.

For the violin plot to appear as it should, the VIOLIN PLOT command is usually preceded by the two commands:

CHARACTERS VIOLIN PLOT
LINES VIOLIN PLOT


These commands automatically define proper values for the 25 components of the violin plot. Note that traces 2 thru 25 correspond to the definitions for the traces in the standard box plot (HELP BOX PLOT for details). Trace 1 draws the kernel density portion.

After the violin plot is formed, the analyst should redefine plot characters and lines via the usual CHARACTERS and LINES commands.

VIOLIN PLOT <y> <x>       <SUBSET/EXCEPT/FOR qualification>
where <y> is the response (= dependent) variable;
            <x> is an independent variable;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

VIOLIN PLOT Y X
VIOLIN PLOT Y X SUBSET X > 2

Outliers on the box plot can be identified by entering the FENCES ON command. If the inter-quartile range (i.e., the difference between the 25% point and the 75% point) is IQ, then values that are between 1.5 and 3.0 times the IQ above (or below) the 75% point (or the 25%) point are drawn as circles and points that are more than 3.0 times the IQ above (or below) the 75% point (or the 25%) are drawn as large circles.

An alternate form for the appearance of the violin plot can be generated by entering the commands CHARACTERS VIOLIN BOX PLOT and LINES VIOLIN BOX PLOT. These draw the traditional form of the box plot rather than the streamlined Tufte form of the box plot.

You can also define your own plot symbols with the standard CHARACTER and LINE commands (e.g., you may prefer to use a dash (-) rather than the default X.

The width of the box is proportional to the number of data points in that box. This only applies if the lines and characters are set to LINES VIOLIN BOX PLOT and CHARACTERS VIOLIN BOX PLOT, respectively. For the default lines and character settings (LINE VIOLIN PLOT, CHARACTERS VIOLIN PLOT), the width of the box is not relevant.

The following commands can be used to set ooptions for the kernel density plot:
KERNEL DENSITY POINTS <value>
KERNEL DENSITY WIDTH <value>


Enter HELP KERNEL DENSITY PLOT for details on these commands.

"Violin Plots: A Box Plot-Density Trace Synergism", Jerry L. Hintze and Ray D. Nelson, The American Statistician, May 1998 Vol. 52, No. 2, 181-184.

None

CHARARCTER VIOLIN TUFTE BOX PLOT is equivalent to CHARACTER VIOLIN PLOT. Similarly, LINES VIOLIN TUFTE BOX PLOT is equivalent to LINE VIOLIN PLOT.

BOX PLOT	= Generate a box plot.
KERNEL DENSITY PLOT	= Generate a kernel density plot.
CHARACTERS	= Sets the types for plot characters.
LINES	= Sets the types for plot lines.
REGION FILL	= Sets the types for plot regions.
PLOT	= Generates a data or function plot.

Hintze and Nelson (1998), "Violin Plots: A Box Plot-Density Trace Synergism," The American Statistician, Vol. 52, No. 2, pp. 181-184.

Exploratory Data Analysis, Comparing Distributions

2/2003

 
SKIP 25
READ DRAFT69B.DAT Y XJUNK X
.
CHARACTER VIOLIN PLOT
LINE VIOLIN PLOT
XLIMITS 1 12
MAJOR XTIC MARK NUMBER 12
MINOR XTIC MARK NUMBER 0
XTIC OFFSET 1 1
X1TIC MARK LABEL FORMAT ALPHA
X1TIC MARK LABEL CONTENT JAN FEB MAR APR MAY JUN JUL AUG SEP OCT ...
   NOV DEC
Y1LABEL DRAFT RANK
KERNEL DENSITY POINTS 32
.
VIOLIN PLOT Y X