"When the Rasch model is intended to hold because of its special measurement properties, failure of the data to conform to the model implies further work on the substantive problem of scale construction, not on the identification of a more complex model that might account for the data."
David Andrich in Rasch Models for Measurement. 1988. p.86. Newbury Park, CA: Sage.

Excerpt from a brochure for Microscale (1984-1986, authors Benjamin D. Wright and John M. Linacre), the first Rasch program that handled missing data. It was PC-based and integrated with either the SuperCalc spreadsheet or the SYSTAT statistical package.

What does a score mean?

How can we turn performance ratings, test results, questionnaires or counts of behavioral activities into measurements with the same meaning as meters or grams have for physical attributes?

This is a major problem which faces many educators, social scientists, pollsters, human resource managers, market research specialists and others attempting to examine attributes which can only be measured indirectly by observing an interaction in some natural or artificial situation.

For instance, the measurement of math competency in a student cannot be done directly, but is generally done by creating the artificial situation of a math test, and observing the interactions between the student and the math questions. The examiner then wants to turn the resulting record of correct and incorrect responses into a measure of the student's competency.

Microscale constructs such measures. These measures have the same characteristics of fundamental measurement that meters and grams have. So that when observations are of a one-dimensional abstraction, such as an individual's competency, attitude or purchasing behavior, using Microscale -

* they can be represented by linear magnitudes

* more or less comparisons can be made directly

* the measuring process is independent of which particular agents and objects take part

* agents and objects can be represented on the same scale

* a unit of measurement anywhere on the scale represents the same amount of change

Quotations … Rasch Measurement Transactions, 1989, 3:1 passim

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: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr. 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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