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A Page About Software

“Yes, we have no bananas”

Much of the software formerly on this page has become obsolete on its own, or has been rendered obsolete by the release of IRTPRO and/or flexMIRT IRT software. Two of our older pieces of software remain: PlotIRT and IRTLRDIF. While IRTPRO provides adequate graphics for most data analysis using IRT, it is sometimes useful to create customized graphics for reports or publications; PlotIRT and the R graphical environment provide flexibility for such purposes. And while either IRTPRO or flexMIRT provide far more extensive, easier-to-use DIF analysis, IRTLRDIF remains available for a time, because it sees widespread use. [I do, however, strongly recommend that all users of IRTLRDIF migrate to IRTPRO or flexMIRT as soon as possible! IRTLRDIF receives no maintenance or support, and will soon be withdrawn.]

PlotIRT: A Collection of R Functions to Plot Curves Associated with Item Response Theory
The PlotIRT set of R functions facilitates plotting a variety of curves associated with item response theory: item and test characteristic curves, item and test information curves, expected item score functions, and posterior density distributions. The user can specify colors, labels, the number of plots in a window, the number of items within a plot, font sizes, and a variety of other options. The R functions are applicable to the two-parameter logistic, three-parameter logistic, graded, nominal, and multiple-choice models. Basic R functions can be used to read in an assortment of item parameter files, or item parameters can be directly typed into R arrays. Plots can be saved as any file type supported by R, including postscript and portable document format. PlotIRT runs on any Windows or Mac-based computer with R installed. R, a free software environment for statistical computing and graphics, can be downloaded from a mirror at Click here to download a .zip file containing the PlotIRT source code, documentation, and example files.
IRTLRDIF is software that computes likelihood ratio tests of DIF for the 3PL and graded IRT models. Click here to download IRTLRDIF 2 for Windows, or Click here to download IRTLRDIF 2 for the Mac OS v 9.x or X. [Note: For Mac OS v. 9.x, if your system does not already have Carbonlib 1.4 or higher, it is necessary to drag the extension "Carbonlib" (included in the .sit file) to the (closed) System folder and then restart the computer.] For either system, the download archive includes the application, a test file, and the documentation in .pdf format.

The authors make no warranties, expressed or implied, about the usefulness for any purpose of the software the can be downloaded from this page. All software downloaded from this page is free, and may be freely distributed. However, the software should not be sold, or used commercially in any way, without the expressed consent of the author(s).

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Last modified 11/14/2014