Center facet =

One facet must be non-centered in most analyses. Center= specifies which facets are to be centered, so that the mean of the element measures is zero (or Umean=). Other facets are non-centered, unless they are anchored or group-anchored. If both Center= and Noncenter= and Center= are specified, only the first encountered in the specification file is actioned. When any element within a facet is anchored, or group-anchored, then the origin of the scale for that facet is set by the anchoring. Both Center= and Noncenter= are ignored for that facet.

 

a)Center= facet number, facet number, ...
a mean element measure of zero (or Umean=) for element measures with non-extreme scores
Example: Center= 2, 3, 4
 

b)Center= facet number Z, facet number Z, ...
a mean element measure of zero (or Umean=) for all element measures, including extreme scores
Example: Center= 2Z, 3Z, 4Z
 

c)Center= facet number, facet number Z, ...
a combination of (a) and (b)
Example: Center= 2, 3Z, 4
 

Extreme measures (corresponding to minimum and maximum possible scores) are included in the Means in Table 7, so that these may not be 0  (or Umean=) for centered facets unless: Center= facet number Z

 

In most analyses, if all facets are centered or anchored, then the estimates are over-constrained and displacements are reported. If more than one facet is non-centered, the frame of reference is not sufficiently constrained and the element measures are ambiguous (non-identified). The usual convention is to center the frame of reference on the agents of measurement: items, tasks, judges. This establishes the origin. Then the objects of measurement, persons, are positioned with respect to this origin. Technically, centering is an identifiability constraint, so that the estimates are uniquely defined.

 

Example 1: facets 2 (items) and 3 (raters) are to be centered; facet 1 is non-centered.

Center= 2, 3 ; non-extreme element measures are centered in facets 2 and 3.

Center= 2Z, 3Z ; all element measures are centered in facets 2 and 3

Center= 2, 3Z ; non-extreme element measures are centered for facet 2; all element measures are centered for facet 3

 

Example 2: No facets are to be centered. This is an unusual situation such as when there is only one active facet so that the item difficulties are defined relative to an implicit origin as in the "Three Mile Island" example.

Center=0


Help for Facets (64-bit) Rasch Measurement and Rasch Analysis Software: www.winsteps.com Author: John Michael Linacre.
 

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Rasch Books and Publications
Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, 2nd Edn, 2024 George Engelhard, Jr. & Jue Wang Applying the Rasch Model (Winsteps, Facets) 4th Ed., Bond, Yan, Heene Advances in Rasch Analyses in the Human Sciences (Winsteps, Facets) 1st Ed., Boone, Staver Advances in Applications of Rasch Measurement in Science Education, X. Liu & W. J. Boone Rasch Analysis in the Human Sciences (Winsteps) Boone, Staver, Yale
Introduction to Many-Facet Rasch Measurement (Facets), Thomas Eckes Statistical Analyses for Language Testers (Facets), Rita Green Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments (Facets), George Engelhard, Jr. & Stefanie Wind Aplicação do Modelo de Rasch (Português), de Bond, Trevor G., Fox, Christine M Appliquer le modèle de Rasch: Défis et pistes de solution (Winsteps) E. Dionne, S. Béland
Exploring Rating Scale Functioning for Survey Research (R, Facets), Stefanie Wind Rasch Measurement: Applications, Khine Winsteps Tutorials - free
Facets Tutorials - free
Many-Facet Rasch Measurement (Facets) - free, J.M. Linacre Fairness, Justice and Language Assessment (Winsteps, Facets), McNamara, Knoch, Fan
Other Rasch-Related Resources: Rasch Measurement YouTube Channel
Rasch Measurement Transactions & Rasch Measurement research papers - free An Introduction to the Rasch Model with Examples in R (eRm, etc.), Debelak, Strobl, Zeigenfuse Rasch Measurement Theory Analysis in R, Wind, Hua Applying the Rasch Model in Social Sciences Using R, Lamprianou El modelo métrico de Rasch: Fundamentación, implementación e interpretación de la medida en ciencias sociales (Spanish Edition), Manuel González-Montesinos M.
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch Rasch Models for Measurement, David Andrich Constructing Measures, Mark Wilson Best Test Design - free, Wright & Stone
Rating Scale Analysis - free, Wright & Masters
Virtual Standard Setting: Setting Cut Scores, Charalambos Kollias Diseño de Mejores Pruebas - free, Spanish Best Test Design A Course in Rasch Measurement Theory, Andrich, Marais Rasch Models in Health, Christensen, Kreiner, Mesba Multivariate and Mixture Distribution Rasch Models, von Davier, Carstensen
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