An Introduction to Rasch Measurement
Rasch measurement is a model-based approach in measurement that has become increasingly popular for scale construction in the social (and other) sciences. Rasch measurement provides a way to convert ordinal observations (raw scores) into linear measures (logits) (Rasch, 1960; Fischer, 1995a; Wright & Mok, 2004), thus making it an important tool in scientific research where phenomena are observed on an ordinal scale and parametric statistics, which assume an interval/ratio scale, are employed for analysis (Wright & Linacre, 1989). This chapter introduces basic concepts of Rasch measurement models and their applications.
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Activities from the chapter:
Example 1
In this example, a Rasch analysis of data obtained from a test of short-term memory of 35 children using 18 items, each of which are scored as correct (1) or incorrect (0) is presented. The WINSTEPS control file for this data set is provided with the installation of the WINSTEPS program. To run a Rasch analysis of this dichotomous data set, open up the WINSTEPS program. At the prompt asking for a control file name, press [Enter]. A control file window will show a list of files from an examples folder. Open a file named “kct.txt”. Then press [Enter] to request a temporary output file. Finally, press [Enter] again to skip providing extra specification. The WINSTEPS program will then start running the analysis, using a Rasch model for dichotomous data. (see chapter for details on executing this analysis properly)
Example 2
In this example, an analysis of a ‘liking for science’ questionnaire using the Rasch rating scale model is presented. This questionnaire asked for ratings of various activities from a group of 75 students using a 3-category rating scale ranging from 0 to 2, where 0 represents ‘dislike’, 1 represents ‘neutral’ (note that we do not advocate the use of a ‘neutral’ option in rating scales due to the potential dangers of using a neutral category), and 2 represents ‘like’. The WINSTEPS control file for this data set is available in the WINSTEPS folder after installation of the program. To run the analysis of this data set using the Rasch rating scale model press [Enter] at the control file prompt after opening the WINSTEPS program. Open the file named “sf.txt”. Then press [Enter] twice. The WINSTEPS program will then run the analysis using the rating scale model. (see chapter for details on executing this analysis properly)