SAS Programs for Formatting Winsteps Input and Output Files

Chong Ho Yu






















































Winsteps (Rasch measurement software and publications, 2003), as its name implies, is a psychometric program created specifically to compute the step function (Wright & Masters, 1982) for exams carrying partial-credit items.  Despite the clarity of the Rasch model (Bond & Fox, 2001) and the availability of rich features, such as the item-person map, Scalogram, and fitness indices, in the program, coding the input file for Winteps, especially the partial-credit key, and interpretation of Winsteps?output, could be challenging to novices. This challenge is partly due to the Winsteps?text-based interface. In order to augment Winsteps, two SAS macros programs were written to aid users by formatting the input file for Winsteps and by adding graphical presentation of the Winsteps item parameter output.

Description is a SAS Macro program (SAS Institute, 2004; Carpenter, 2004) written to automatically format a complete control file ready to be run by Winsteps with the proper partial-credit key format. Users can store the key for an exam in the format as shown in Figure 1 and the partial-credit key will be output as shown in Figure 2:

Figure 1. Partial-credit key as an input string


 Figure 2. Partial-credit key in the Winsteps format


Nevertheless, if all items in the exam are dichotomously-scored, the SAS program will output a binary key. A document entitled sf.html is included with the package to help beginners to interpret the step function yielded from partial-credit items., which is also written in SAS Macros, is a program for generating graphical presentations, such as the Test Information Function (TIF), Item Information Function (IIF), Test Characteristic Curve (TCC), and Item Characteristic Curve (ICC). This SAS program can import the question/item parameter output and utilize its item parameter information to create the exam-level report named report.html. This Web-based output file presents the global overview of the exam by illustrating TIF, TCC, and the distribution of item parameters. Although Winsteps provides the item-person map with item ID and subject ID on each datum point to users, the ID is represented by the symbol “X" or the other symbols when there are too many items and/or subjects in the dataset. Nonetheless, the SAS graph has the feature of revealing information at “mouse over,?namely, when the user moves the cursor on top of one of the bars depicting an item parameter, the item ID pops up.

In addition, each item shown on the report page contains a hotlink to a HTML page overlaying ICC and IIF together. If the question is a partial-credit item, the HTML page will present the step function in both graphical and tabulated forms. This hyper-link feature enables test developers to visually inspect item attributes in a more efficient fashion. In addition, the report and graphs are Web-ready and thus the results can be shared among colleagues through the Internet or IntraNet. A document entitled IRT.pdf is attached to the package for helping beginners to interpret ICC, TCC, IIF and TIF.

Both SAS Macros programs require SAS Version 9.1.3 for Windows since the latest features of ODS and Macros are used. Nevertheless, even if the viewer does not have SAS in the client computer, the SAS Graph Viewer is freely downloadable from In the second SAS program, the device driver for outputting SAS graphs is set as "ActiveX," which is embedded in Internet Explorer, but not in other browsers. If the target audience does not use Internet Explorer, it is advisable to replace "ActiveX" with "Actximg" (ActiveX Image) or “Java." ActiveX Image renders the image in the PNG format, which is supported by all Web browsers while Java is available for no cost from


The program, the documents, and the sample input/output files is freely downloadable.


Bond, T. G., & Fox, C. M. (2001). Apply the Rasch Model: Fundamental measurement in the human sciences. Mahwah, NJ: Lawrence Erlbaum Associates.

Carpenter, A. (2004). Carpenter’s complete guide to the SAS Macro Language. Cary, NC: SAS Institute.

Rasch measurement software and publications. (2003). Winsteps [Computer software]. [On-line] Available URL:

SAS Institute. (2004). SAS 9.1.3 [Computer Software]. Cary, NC: The Author.

Wright, B. D., & Masters, G. N. (1982). Rating scale analysis. Chicago, IL: MESA Press.




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