Frame of reference
The observations are understood to be the result of stochastic interactions between elements of facets. Each element is to be measured or calibrated within a common frame of reference. This frame of reference must be defined. There are three decisions:
Usually the origin of the scale, the "zero" point for each facet, is set at the mean value of the measures for that facet, i.e., centered. When this has been done for all facets except one, the placement of the origin for that last facet is then determined by the data. That facet will be non-centered=.
Usually the noncenter= facet is the examinees.
Does a greater raw score correspond to a greater measure? This positive orientation is usually how person abilities and judge leniencies are conceptualized.
Does a greater raw score correspond to a lesser measure? This negative orientation is usually how item and task difficulties and judge severities are conceptualized.
In some analyses, there is only one positively oriented facet, the measured people. All other facets are negatively oriented: item difficulty, judge severity, task challenge etc.
In other analysis, all facets are positively oriented. person ability, item easiness, judge leniency, task facility.
Careful choice of facet orientation avoids confusion in interpreting Facets output.
c) What is the unit of measurement? Umean=
The conventional Rasch unit of measurement is the "Logit", and this the standard unit. It is often convenient, however, to linearly rescale the logit into RITS, WITS, or to give the measures a useful range, e.g., 0 - 100 (see BTD chapter 8). Umean= accomplishes this.
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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|
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|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|
|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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