Monday, January 2, 2012

The Separation Plotter

Recently, Brian Greenhill, Michael Ward and Audrey Sacks published an article in the American Journal of Political Science titled The Separation Plot: A New Visual Method for Evaluating the Fit of Binary Models

They propose a powerful visual method for showing the predictive value of binary regression models.  Unfortunatly, the program that they provide to generate "Separation Plots" is embeded within R.  While R is a fantastic statistical program, it is not widely used in politcal science.  So, for those of us who use Stata, SAS, SPSS, or some other program, I have developed a stand alone windows based computer program that can generate separation plots.

The program should be intuitive to use.  Users can load .csv files that contain an outcome variable and a predicted probability variable (most statistical software packages can export data as .csv).  Once the data is loaded, the user identifies the outcome and probability variables under the "variable view" tab.   The user sets the properties desired for the separation plot and then selects the option to "Generate Graph" under the File menu.  The plot can then be saved as a .jpg image file.

I have done quite a bit of testing and de-bugging, but if you encounter problems with the program please let me know.


Most Recent Version (including Microsoft's VB Powerpack)
Separation Plotter Download

(I have been having problems running the program on other machines that do not have Microsoft's VB Powerpack already installed.  Thus, I have included this in the installation package.  The instalation file may need to be run twice before the install file recognizes the VB Powerpack has actaully been installed.)


Known Bugs:  
I have resolved the issue with the program crashing in response to very large files.  However, a new issue relating to the placement of expected number of events marker has arisen.  This issue can be fixed with a bit of image editing (or simply selecting the option to not use a marker for expected events), but I will try to fix the placement in the code.

Update: I have been notified of a memory issue that can occur with the separation plotter (particularly when using the default width setting), I am still in the process of nailing down all the related bugs to this issue but a greatly improved version was posted on October 27th 2012.

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