Rasch analysis software

Danish mathematician George Rasch developed the Rasch model (5). Researchers can use the Rasch model to develop tests and surveys, monitor the quality of survey or test data, improve test or survey items, and calculate an equal interval total score for both test takers and survey respondents. When researchers evaluate data using parametric statistical tests (e.g., t-test, ANOVA), they assume that score data is " equal interval. We can use the Rasch analysis software to convert non-equal interval data into equal interval data. In recent years, evaluators have used the Rasch model for large-scale, assessment projects such as the evaluation of reform in the Chicago Public Schools (6)... 

Figure 1 showed how item authors could predict the difficulty of test items, in order to develop a test (or survey) with a range of items. Rasch analysis software produces item maps which allow researchers to evaluate the distribution of items on a test from easy to hard and to identify possible gaps in item difficulty. An optimum test will have items with various difficulties rather than many items of the same difficulty. Researchers can also use item maps to communicate how different groups (e.g., girls and boys) perform on particular test measures. Figure 3 shows an example of an item map. 

By conducting a Rasch analysis of basic test (or survey) data, researchers can quickly convert possibly non-equal interval raw data to interval data. To best understand this issue, consider the following Sarah completes a test and earns 95/100, while Pam emis 90/100. The difference between Sarah and Pam may not necessarily be the same as the difference between Tom who earns 50/100 and Henry who scores 55/100. Although the differences (5 points in each case) between the raw scores are the same, the raw score at different parts of the scale may not have die same substantive meaning. Rasch analysis software can be easily used to convert the possibly non-interval raw score data of tests and surveys to an interval scale, and it is that data which is used for statistical analyses. 

Several software programs support Rasch analysis. Winsteps (7) is user-friendly and the author provides technical support via email. Numerous Winsteps workshops are regularly offered throu out the world. Below we provide a very simple control fde that can be used to evaluate a ten-item, multiple-choice data set. We have provided comments throughout the sample control file. Our intention is to show readers a simple Rasch analysis with a small amount of understandable code. The Winsteps software site also provides free Rasch software called Ministeps (7). Researchers can use Ministeps for a Rasch analysis of data. 

Winsteps (Winsteps download includes Ministeps). [Rasch Measurement Analysis Software]. Retrieved from http //www.winsteps.com/rasch.htm. 

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