[Rasch] 4 vs 1 dimension

Juanito Talili talilij at yahoo.com
Thu Jan 22 16:58:23 EST 2009

I thought that each subscale is a dimension.  Thereby, there are 4 dimensions since the entire instrument has 4 subscales.  I dont know if this thinking is right.

--- On Thu, 1/22/09, Stephanou, Andrew <Stephanou at acer.edu.au> wrote:

From: Stephanou, Andrew <Stephanou at acer.edu.au>
Subject: RE: [Rasch] 4 vs 1 dimension
To: talilij at yahoo.com
Date: Thursday, 22 January, 2009, 5:39 AM

"Though I know that the instrument has 4 dimensions"
How do you know?  Isn't this only an assumption?


From: rasch-bounces at acer.edu.au on behalf of Juanito Talili
Sent: Wed 1/21/2009 5:10 PM
To: rasch
Subject: [Rasch] 4 vs 1 dimension

The 50-item instrument has 4 subscales where each subscale has 2 to 15 items
quantified using 4-point ordinal scale coded 1=strongly disagree to 4=strongly
agree.  Though I know that the instrument has 4 dimensions, I've tried to
test the unidimensionality of the overall 50 items.  Using Winsteps, the % of
variance explained is somewhat acceptable (>75%) for a unidimensional
assumption.  Am I wrong if I do Rasch analysis for the entire instrument rather
than Rasch analysis for each domain?


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