Question: Is it good practice for me to supply a lookup table or Excel sheet to convert sum scores into the measure scores so that users get their results on an interval scale? Is there a good example to cite?
Answer: Many publishers and authors supply a "raw score to scale score" conversion chart. It is convenient for the users, and also allows different versions and revisions of the instrument to continue to generate comparable scale scores. Here is an example showing raw scores and their Rasch logit equivalents:
|Hsueh I-P., Wang W.-C., Sheu C.-F., and Hsieh C.-L. (2004) Rasch Analysis of Combining Two Indices to Assess Comprehensive ADL Function in Stroke Patients. Stroke, 35(3): 721 - 726.|
But it is more useful to publish a transformation of Rasch logits, not the logits themselves. Transform the logits such that all Rasch "scores" are reported as positive integers. Here is a rescaled example. You can note the exact logit transformation as a footnote to the Table if it will be meaningful to your readers.
|Ohio Department of Education, Office of Assessment|
Raw Score-to-Measure (Scaled Score) Tables. Rasch Measurement Transactions, 2007, 21:1 p. 1095
|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|
|Forum||Rasch Measurement Forum to discuss any Rasch-related topic|
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