[Rasch] Why are Rasch measures linear?

commons commons at tiac.net
Tue Sep 4 12:05:18 EST 2007

I have tried to do this with Rasch scaled stage scores and Orders of
Hierarchical Complexity.  One might think that the orders of hierarchical
complexity would all be equal distanced because each higher order organizes
two or more less hierarchically complex actions.  This is true of all
orders.  But we treat the order of hierarchical complexity as an ordinal.
Empirically we do not get equal spacing on the Rasch scale of item from the
same sequence.





From: rasch-bounces at acer.edu.au [mailto:rasch-bounces at acer.edu.au] On Behalf
Of Trevor Bond
Sent: Monday, September 03, 2007 9:00 PM
To: Stephanou, Andrew; Paul Barrett; rasch at acer.edu.au
Subject: RE: [Rasch] Why are Rasch measures linear?


<Perhaps it is a two-stage process - construct a Rasch variable, then seek
to confirm the linear properties via other kinds of empirical observations
where linear magnitudes of the variable should yield specific, related,
magnitudes of other outcomes - in contrast to simple sumscore or other kinds
of magnitude scoring (ordinal classes etc.).>


Paul's two measurement parts:

a the Rasch bit...which is what the original question was about and

b the theoretical psychological epistemological philosophical bit which only
a few even concern themselves with...but Paul obsesses about


While we a doing a, we should never forget the challenge of trying to do b


We can use the excuse: No one else gives a rodent's posterior so why should


but following that logic we would not be using Rasch measurement would we?


As for aligning our units with the underlying neuro-physiological
electro-chemical processes...give us a break!


with a smile



Trevor G BOND Ph D
Professor and Head of Dept
Educational Psychology, Counselling & Learning Needs

D2-2F-01A EPCL Dept.
Hong Kong Institute of Education
10 Lo Ping Rd, Tai Po
New Territories HONG KONG

Voice: (852) 2948 8473
Fax:  (852) 2948 7983


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