[Rasch] formative v. reflective measures in assessment research

Michael Lamport Commons commons at tiac.net
Sat Oct 26 07:04:45 EST 2013

Difficulty will Rasch analyze as a single dimension.  But there may be 
many sources of difficulty, "Order of Hierarchical Complexity, size of 
numbers used in calculations, length of sentences.

On 10/25/2013 1:57 PM, Donald Bacon wrote:
> Hi all --
>    The Rasch model assumes that each measure in a scale reflects the 
> same underlying trait, and so it seems that a reflective measurement 
> model is appropriate, and internal consistency is a desirable 
> quality.  But what about the case of a long comprehensive exam, such 
> as one we might use for assessment.  In my experience, these exams 
> often behave as if they were close to unidimensional, even though many 
> different learning outcomes are captured.  If well designed, these 
> tests often exhibit high internal consistency.  Because the models fit 
> well, I've always thought of the measures as reflective, but perhaps 
> my theory is wrong even though the fit is good; maybe the measures are 
> formative.  Is there any way to use the Rasch model with formative 
> indicators?
> Thanks for any insights you might have --
> Don
> Donald R. Bacon, Ph.D.
> Professor of Marketing
> Editor, Journal of Marketing Education
> Daniels College of Business
> University of Denver
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> Rasch at acer.edu.au
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My Best,

Michael Lamport Commons, Ph.D.
Assistant Clinical Professor

Department of Psychiatry
Beth Israel Deaconess Medical Center
Harvard Medical School
234 Huron Avenue
Cambridge, MA 02138-1328

Telephone  (617) 497-5270
Facsimile   (617) 491-5270
Cellular      (617) 320 0896
Commons at tiac.net
Skype: MichaelLCommons

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