How to Show Grouping in Scatterplots

STATISTICA how-to logoA scatterplot shows the relationship between continuous variables. Applying a grouping factor adds yet another dimension that can greatly enhance a plot’s usefulness.
This article explores two ways of showing a grouping variable in a scatterplot. The difference between the two methods is the fit line. One method uses one fit for all levels of a grouping factor, but shows the levels with point marker colors and patterns. The other method fits separate lines for each group.
The data set used in this example, Irisdat.sta, contains measurements for various parts of the flower for three different varieties of iris. To open the data set, select the Home tab and in the File group, click the Open arrow. From the menu, select Open Examples to display the Open a STATISTICA Data File dialog box. Double-click the Datasets folder, and then open Irisdat.sta.
One Fit Line for All Groups
Select the Graphs tab. In the Common group, click Scatterplot to display the 2D Scatterplots Startup Panel. Click the Variables button to display the Select Variables for Scatterplots dialog box, and select SEPALLEN as X and SEPALWID as Y.
STATISTICA - Select variables for Scatterplot
Click the OK button.
On the Advanced tab of the 2D Scatterplots Startup Panel,
STATISTICA - 2D Scatterplot startup panel
click the Mark Selected Subsets button. The Specify Multiple Subsets dialog box will be displayed. Create the three subsets for the grouping factor, IRISTYPE, as shown in the next image.
STATISTICA - Specify multiple subsets dialog
Click OK in the Specify Multiple Subsets dialog box, and click OK in the 2D Scatterplots Startup Panel.
The resulting graph is a scatterplot that contains one fit line for all points, but distinguishes points by the grouping variable IRISTYPE with colors and point markers.
STATISTICA - Scatterplot with one fit line for all points
Separate Fit Lines for Groups
Alternatively, it may be appropriate to use separate fit lines for the three groups. To do this, create a categorized graph.
Start a new 2D Scatterplots analysis, and select variables as before.
Now, in the 2D Scatterplots Startup Panel, select the Categorized tab. In the X-Categories group box, select the On check box. The options will become active. Click the Change Variable button to display the Select Categorization Variable dialog box. Select IRISTYPE.
STATISTICA - Select Categorization Variable dialog
Click OK to close this dialog box and return to the 2D Scatterplots Startup Panel.
The options Integer mode, Unique values, Categories, etc., give you flexibility with the grouping variable. A categorization variable does not have to be categorical in nature.
In the Layout group box, select the Overlaid option button.
STATISTICA - 2D Scatterplot startup panel again
Click OK to create the graph. Three separate fit lines are shown for the three categories in addition to the groups being designated by colors and point markers.
STATISTICA - Scatterplot with three separate fit lines - categorized
STATISTICA graphs offer extensive flexibility, which enables you to create the representation of the data that you need.
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About statsoftsa

StatSoft, Inc. was founded in 1984 and is now one of the largest global providers of analytic software worldwide. StatSoft is also the largest manufacturer of enterprise-wide quality control and improvement software systems in the world, and the only company capable of supporting its QC products worldwide, with wholly owned subsidiaries in all major markets (StatSoft has 23 full-service offices, on all continents), and its software is available in more than 10 languages.

Posted on April 15, 2014, in Uncategorized. Bookmark the permalink. Leave a comment.

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