﻿ Measures and calibrations

# Measures and calibrations

Various terms are used for the Rasch-model parameter estimates associated with each element.

Measures: this is the general term used to indicate the values of the estimates in a linear, interval, additive, frame of reference.

Logit values: the natural values for Rasch estimates are in "log-odds units" or logits. Logit differences have a direct relationship to probabilities for dichotomous items. For polytomous items, the probabilistic relationship is conditional.

Rescaled or user-scaled values: logit values can be rescaled linearly, i.e., by adding a constant amount and multiplying by a constant amount. The rescaled values maintain their linear quality. These are set with Umean=

Calibrations or difficulties: these are measures for items.

Abilities: these are measures for persons.

In dichotomous situations, the measure is the point on the latent variable at which there is a 50% probability of success or failure when encountering a person, item or other element known to be at that point on the variable.

In polytomous situations, the measure is the point on the latent variable at which there is an equal probability (however small) of being observed in the top or bottom polytomous category when encountering a person, item or other element known to be at that point on the variable.

The standard reference point for a dichotomy or polytomy can be altered by using structure anchoring, Rating scale=.

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Rasch Publications
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
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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
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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
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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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