In some data designs, data are collected from the same persons more than once, or observations are collected on equivalent items. Consequently there is reason to suspect that local dependence exists in the data. What is its impact on the Rasch measures?
Local dependence usually squeezes or stretches the logit measures, but does not usually change cut-points much when they are expressed in raw-score terms.
Procedure A. If a subset of items may have strong local dependence, then rescore the subset as one partial-credit item.
1) Analyze all the data with subset of items as separate items. Output the person measures to Excel. PFILE=
2) Combine the scores on the subset of items into one partial credit item. All the other items remain unchanged. Analyze all the data. Output the person measures to Excel. PFILE=
3) In Excel, cross-plot the person measures from (1) and (2). The curvature of the plot shows the influence of the local dependence on linearity.
4) Is the curvature big enough to be important to your audience? If yes, use the person measures from (3). If no, use the person measures from (2). My guess is usually "No".
Procedure B. To avoid local dependence in measuring change from pre-test to post-test:
1.Create a random, "stacked" dataset, in which each patient only appears once, either at pre-test or post-test. For instance, see FORMAT= example 7.
4.Run Winsteps on the full post-test data set using the IAFILE-if.txt and SAFILE=sf.txt from step #2
5. You can determine the effect of local dependence by cross-plotting the person measures from 3) and 4) against the measures from an unanchored stacked analysis of all the data.
Marais I. Response dependence and the measurement of change. J Appl Meas. 2009;10(1):17-29
Procedure C. Here is an experiment to determine whether local dependence is a problem. Assuming that data from the same persons may be a problem, select from your cases one of each different response string. This will make the data as heterogeneous as possible. Perform an analysis of this data set and see if that changes your conclusions markedly. If it does, then local dependence may be a concern. If it doesn't then local dependence is having no substantive impact.
Using Excel, a method of obtaining only one of each different response string:
0. Import the data into excel as a "character" column
1. from the Excel data pull down menu choose -> filter -> advanced filter
2. under "action" choose "copy to another location"
3. click "list range" and highlight the range of element numbers - if you want the whole column click on the letter at the top of the column
4. click "copy to" and choose an empty column, e.g., column J.
5. click "unique records only"
6. click "OK"
7. look at column J. The data are unique.
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|Rasch Measurement Transactions (free, online)||Rasch Measurement research papers (free, online)||Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch||Applying the Rasch Model 3rd. Ed., Bond & Fox||Best Test Design, Wright & Stone|
|Rating Scale Analysis, Wright & Masters||Introduction to Rasch Measurement, E. Smith & R. Smith||Introduction to Many-Facet Rasch Measurement, Thomas Eckes||Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments, George Engelhard, Jr. & Stefanie Wind||Statistical Analyses for Language Testers, Rita Green|
|Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar||Journal of Applied Measurement||Rasch models for measurement, David Andrich||Constructing Measures, Mark Wilson||Rasch Analysis in the Human Sciences, Boone, Stave, Yale|
|in Spanish:||Análisis de Rasch para todos, Agustín Tristán||Mediciones, Posicionamientos y Diagnósticos Competitivos, Juan Ramón Oreja Rodríguez|
|Winsteps Tutorials||Facets Tutorials||Rasch Discussion Groups|
|Coming Rasch-related Events|
|Jan. 5 - Feb. 2, 2018, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com|
|Jan. 10-16, 2018, Wed.-Tues.||In-person workshop: Advanced Course in Rasch Measurement Theory and the application of RUMM2030, Perth, Australia (D. Andrich), Announcement|
|Jan. 17-19, 2018, Wed.-Fri.||Rasch Conference: Seventh International Conference on Probabilistic Models for Measurement, Matilda Bay Club, Perth, Australia, Website|
|Jan. 22-24, 2018, Mon-Wed.||In-person workshop: Rasch Measurement for Everybody en español (A. Tristan, Winsteps), San Luis Potosi, Mexico. www.ieia.com.mx|
|April 10-12, 2018, Tues.-Thurs.||Rasch Conference: IOMW, New York, NY, www.iomw.org|
|April 13-17, 2018, Fri.-Tues.||AERA, New York, NY, www.aera.net|
|May 22 - 24, 2018, Tues.-Thur.||EALTA 2018 pre-conference workshop (Introduction to Rasch measurement using WINSTEPS and FACETS, Thomas Eckes & Frank Weiss-Motz), https://ealta2018.testdaf.de|
|May 25 - June 22, 2018, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com|
|June 27 - 29, 2018, Wed.-Fri.||Measurement at the Crossroads: History, philosophy and sociology of measurement, Paris, France., https://measurement2018.sciencesconf.org|
|June 29 - July 27, 2018, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com|
|July 25 - July 27, 2018, Wed.-Fri.||Pacific-Rim Objective Measurement Symposium (PROMS), (Preconference workshops July 23-24, 2018) Fudan University, Shanghai, China "Applying Rasch Measurement in Language Assessment and across the Human Sciences" www.promsociety.org|
|Aug. 10 - Sept. 7, 2018, Fri.-Fri.||On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com|
|Sept. 3 - 6, 2018, Mon.-Thurs.||IMEKO World Congress, Belfast, Northern Ireland www.imeko2018.org|
|Oct. 12 - Nov. 9, 2018, Fri.-Fri.||On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com|
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