STRIP PLOT

... STRIP PLOT

Graphics Command

Generates a strip plot (also known as a dot plot).

A strip plot is a graphical data anlysis technique for summarizing a univariate data set. The strip plot consists of:
Horizontal axis = the value of the response variable;
Verticalal axis = all values are set to 1.


That is, a strip plot is simply a plot of the sorted response values along one axis. The strip plot is an alternative to a histogram or a density plot. It is typically used for small data sets (histograms and density plots are typically preferred for larger data sets).

There are a few variations supported for the strip plot.

1. One problem with strip plots is how to display multiple points with the same value. Dataplot provides two options to address this.
   1. With the jitter option, a small amount of random noise is added to the vertical coordinate.

   2. With the stack option, repeated values add a fixed increment to the vertical coordinate. So if there are 3 points with the same value, the y coordinates might be 1, 1.1, and 1.2. This gives the strip plot a histogram-like appearance.

      The value of the fixed increment can be set with the command

      SET STRIP PLOT INCREMENT <value>

      The default value is 1, although a value of on the order of 0.1 is often desirable. This command can be used with the YLIMITS command and the CHARACTER SIZE command to generate the desired appearance for the plot.

      You can specify your preference with the command

      SET STRIP PLOT STYLE

      The default value is STACK.

2. The strip plot can be generated with a group-id variable. For this variant, the y coordinate is is set equal to the corresponding value of the group-id variable. This results in a set of parallel strip plots.

3. You can generate a strip plot with binned data. In this case, the STACK option is automatically used. This option is essentially an alternative form for a histogram. Binned data can also be grouped.

   You can bin your data with the command

   LET Y2 X2 = BINNED Y

   The binning algorithm can be controlled with the commands

   CLASS LOWER <value>
   CLASS UPPER <value>
   CLASS WIDTH <value>
   

STRIP PLOT <y>             <SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
and where the <SUBSET/EXCEPT/FOR qualification is optional.

This syntax is used when you have raw data with a single group.

STRIP PLOT <y> <x>             <SUBSET/EXCEPT/FOR qualification>
where <y> is the variable of pre-computed frequencies;
            <x> is the variable containing the class mid-points;
and where the <SUBSET/EXCEPT/FOR qualification is optional.

This syntax is used when you have binned data with a single group.

BATCH STRIP PLOT <y> <tag>             <SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
            <tag> is a group-id variable;
and where the <SUBSET/EXCEPT/FOR qualification is optional.

This syntax is used when you have raw data with multiple groups.

The word BATCH is required here to distinguish the multiple groups case from the binned data case.

BATCH STRIP PLOT <y> <x> <tag>
                                       <SUBSET/EXCEPT/FOR qualification>
where <y> is the variable of pre-computed frequencies;
            <x> is the variable containing the class mid-points;
            <tag> is a group-id variable;
and where the <SUBSET/EXCEPT/FOR qualification is optional.

This syntax is used when you have binned data with multiple groups.

In this case, the word BATCH is optional.

BATCH MULTIPLE STRIP PLOT <y> <tag1> <tag2>
                                                <SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
            <tag1> is a group-id variable;
            <tag2> is a group-id variable;
and where the <SUBSET/EXCEPT/FOR qualification is optional.

This syntax is used when you have raw data with two group-id variables.

The first group-id variable works as in Syntax 3. That is, it defines the position on the y-axis. The second group-id variable is used to identify multiple curves within the first group-id variable. Appropriate settings for the the CHARACTER command and its various attribute setting commands can be used to highlight the different sub-groups within a group. This option is demonstrated with the Program 4 example below.

STRIP PLOT Y
STRIP PLOT Y SUBSET Y > 2
STRIP PLOT Y X

The appearance of the strip plot can be controlled by appropriate settings for the CHARACTER command (and its attributes).

This is demonstrated in the sample programs below.

None

None

HISTOGRAM	= Generates a histogram.
FREQUENCY PLOT	= Generates a frequency plot.
CLASS LOWER	= Sets the lower class minimum for histograms, frequency plots, and pie charts.
CLASS UPPER	= Sets the upper class maximum for histograms, frequency plots, and pie charts.
CLASS WIDTH	= Sets the class width for histograms, frequency plots, and pie charts.
HISTOGRAM CLASS WIDTH	= Specify alternative default class wdith algorithms for histograms.
LIMITS	= Sets the frame limits for all plots.
CHARACTERS	= Sets the character symbol for plots.

"Standard Practice for Statistical Analysis of One-Sample and Two-Sample Interlaboratory Proficiency Testing Programs", 2006, ASTM International, 100 Barr Harbor Drive, PO BOX C700, West Conshohoceken, PA 19428-2959, USA.

Unwin, Theus, and Hofmann (2006), "Graphics of Large Datasets: Visualizing a Million", Springer, p. 36.

Data Analysis

11/2008
10/2009: Added support for a "BATCH MULTIPLE" option

 
.
.  Step 1: Read the data
.
skip 25
read E2489A.DAT labid y
.
title case asis
title offset 2
label
x2frame off
y2frame off
char circle all
char hw 1 0.75 all
char fill on all
line blank all
tic offset units data
tic offset 0 0
xtic offset 0.2 0.2
.
set strip plot increment 0.1
set strip plot style stack
.
multiplot corner coordiantes 5 5 95 95
multiplot scale factor 2 1
multiplot 2 1
.
.  Step 2a: Generate the strip plot for unbinned data
.           (with one group) Stack Option
.
ylimits 0 2
y1tic marks off
y1tic mark labels off
y1frame off
title Strip Plot - Stacked, Single Group
y1label Number of Occurrences
x1label Data Values
label case asis
strip plot y
.
.  Step 2b: Generate the strip plot for unbinned data
.           (with one group) Jitter Option
.
set strip plot style jitter
.
title Strip Plot - Jittered, Single Group
x1label Data Values
strip plot y
.
end of multiplot
    

 
.
.  Step 1: Read the data
.
skip 25
read gear.dat y x
.
title case asis
title offset 2
label
x2frame off
y2frame off
char circle all
char hw 1 0.75 all
char fill on all
line blank all
.
set strip plot increment 0.15
set strip plot style stack
.
ylimits 1 10
major ytic mark number 10
minor ytic mark number 0
y1tic mark offset 1 1
tic offset unit data
ygrid on
title Strip Plot - Stacked, Multiple Groups
y1label Batch Number
x1label Data Values
label case asis
xlimits 0.98 1.02
major xtic mark number 5
minor xtic mark number 1
xtic mark offset 0.002 0.002
.
batch strip plot y x
    

 
.
.  Step 1: Read the data
.
skip 25
read E2489A.DAT labid y
.
.  Step 2: Bin the data
.
class lower 0.0
class upper 5.0
class width 0.1
let y2 x2 = binned y
.
.  Step 3: Define the appearance of the plot
.
title case asis
title offset 2
label
x2frame off
y2frame off
char circle all
char hw 1 0.75 all
char fill on all
line blank all
tic offset units data
tic offset 0 0
xtic offset 0.2 0.2
.
ylimits 0.8 2
y1tic marks off
y1tic mark labels off
y1frame off
title Strip Plot - Single Group with Binned Data
y1label Number of Occurrences
x1label Data Values
label case asis
.
.  Step 4: Generate the strip plot
.
frame corner coordinate 15 35 85 70
set strip plot increment 0.1
set strip plot style stack
strip plot y2 x2
    

 
.  Step 1: Read the data
.
skip 25
read ripken.dat y x1 x2
.
.  Step 2: Set Plot Options
.
title case asis
title offset 2
label
x2frame off
y2frame off
char circle all
char hw 1 0.75 all
char fill on all
char color red blue green red blue green red blue green
line blank all
.
tic offset unit data
ylimits 1 3
major ytic mark number 3
minor ytic mark number 0
y1tic mark label format alpha
y1tic mark label content Inside Middle Outside
y1label Horizontal Location
y1tic mark offset 0.2  0.2
ygrid on
grid pattern dotted
x1label Batting Average
label case asis
tic mark label case asis
xlimits 0 1
major xtic mark number 6
minor xtic mark number 1
xtic mark offset 0.05 0.05
x3label Vertical Location: Red = Low, Blue = Middle, Green = High
.
.  Step 3: Generate the Strip Plot
.
set strip plot increment 0.1
. set strip plot style stack
set strip plot style jitter
title Strip Plot - Stacked, Multiple Batch Option
batch multiple strip plot y x1 x2