[Rasch] Unidimensionality

Michael Lamport Commons commons at tiac.net
Fri May 9 01:41:12 EST 2008

I am unclear.  If difficulty is decomposable, does that mean Rasch is not a good way to go.


-----Original Message-----
>From: Trevor Bond <trevor.bond at jcu.edu.au>
>Sent: May 8, 2008 10:59 AM
>To: markus.quandt at gesis.org, rasch at acer.edu.au
>Subject: Re: [Rasch] Unidimensionality
>BUT such additional dimensions do not invalidate the use of the Rasch 
>scores, as these have already separated out the ability dimension of 
>oh - but they do invalidate it as providing MEASURES /(Rasch scores)
>N is the sufficient statistic for ability only to the extent that the 
>data fit the model.
>remaining structures in the residuals tell us that the Rasch 
>dimension is not all (most / enough) of what is in the data set.
>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
>Rasch mailing list
>Rasch at acer.edu.au

My best,

Michael Lamport Commons, Ph.D.

Assistant Clinical Professor
Department of Psychiatry
Harvard Medical School

Program in Psychiatry and the Law
Beth Israel Deaconess Medical Center
commons at tiac.net

617-497-5270 Telephone
617-491-5270 Fax

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