[Rasch] Why are Rasch measures linear?

Trevor Bond trevor.bond at jcu.edu.au
Tue Sep 4 11:00:17 EST 2007

><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 

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 we?

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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