Medical Multidimensionality

Unidimensionality is essential to utility. Yet anything examined closely is multidimensional. Nevertheless, a variable can be treated as having one basic meaning so long as the inevitable heterogeneity in manifestations of the variable do not confuse measurement in any conspicuous way. Examination of the Level of Rehabilitation Scale (LORS-III, Formations in Health Care, Inc.) discovered such a conspicuous confusion.

The 27 items of LORS-III are rated by a patient's nurses and therapists at admission to rehabilitation and at discharge. Two items are mainly diagnostic. We examined the other 25 for their utility in defining a stable variable by calibrating the item difficulties with a sample of 3,060 patients at admission and discharge.

The LORS-III plot shows the result. Item calibrations define two conspicuously different lines. The first letter in each item code indicates item focus: "A" is Activity of daily living, "M" is Mobility, "C" is Communication, "G" is coGnition. The second letter identifies the observed process, e.g., "F" is Feeding. The third letter represents the rater, "N" for Nurse, "T" for Therapist, "S" for Speech pathologist. Thus "CWT" is Communication in Written expression rated by a Therapist.

The conspicuous difference between the two variable lines in the calibration plot brings out a confusion in the meaning of the measure. A one logit change from admission to discharge means less improvement on the activity "A" and "M" items, than on the mental "C" and "G" items. Since accurate measurement is essential to determining patient status, therapy effectiveness, and even hospital payment, measures with this degree of ambiguity are impractical. A similar finding has been reported for the FIM (Granger et al. 1993).

This motivated us to examine the activity and mental items separately. Calibrations of the activity items alone, at admission and discharge, are shown in the Activity plot. Now the item calibrations follow the identity line. "AFT" - Activity of Feeding rated by Therapist is a mild outlier. Since therapists do not feed patients, they may not know exactly how much help patients need.

We also calibrated the mental items alone at admission and discharge. Their calibration plot also follows one line, but tilted slightly from the identity line. It seems that raters are better able to discriminate patient functioning at discharge than at admission. This spreads out item difficulties. This is most likely an effect of increased familiarity with patients, and greater patient motivation to exhibit their actual functional levels. On admission, shy patients will appear less functional in higher communication skills than their actual capacities. On this logic, the discharge item calibrations are more valid than the admission ones. Further, since the decision to discontinue rehabilitation depends on discharge measures, they are more important to the patient. Since the measurement of improvement requires the same measurement system at admission and discharge, the discharge system is preferred for its usefulness.

Magalhaes L, Velozo C, Pan A-W, Weeks D. (1993) Medical Multidimensionality. Rasch Measurement Transactions, 7:1 p.265-6.

Granger C.V., et al. (1993) Performance profiles of the Functional Independence Measure. American Journal of Physical Medicine and Rehabilitation 72:2, 84-89.

Medical multidimensionality. Magalhaes L, Velozo C, Pan A-W, Weeks D. … Rasch Measurement Transactions, 1993, 7:1 p.265

Rasch Books and Publications
Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, 2nd Edn. 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

Forum

Rasch Measurement Forum to discuss any Rasch-related topic

Go to Top of Page
Go to index of all Rasch Measurement Transactions
AERA members: Join the Rasch Measurement SIG and receive the printed version of RMT
Some back issues of RMT are available as bound volumes
Subscribe to Journal of Applied Measurement

Go to Institute for Objective Measurement Home Page. The Rasch Measurement SIG (AERA) thanks the Institute for Objective Measurement for inviting the publication of Rasch Measurement Transactions on the Institute's website, www.rasch.org.

The URL of this page is www.rasch.org/rmt/rmt71a.htm

Website: www.rasch.org/rmt/contents.htm