[Rasch] Rsch and CFA

David Andrich david.andrich at uwa.edu.au
Wed Jun 13 12:11:57 EST 2012

Anthony. Regarding point 1 of your question, have a look at
Andrich, D. (1978). Relationships between the Thurstone and Rasch approaches to item scaling. Applied Psychological Measurement,  2 (2), 449-460.
You will see how the error can be seen from a CTT perspective in the probabilistic response.

David Andrich, BSc MEd W.Aust., PhD Chic, FASSA
Chapple Professor
david.andrich at uwa.edu.au<mailto:david.andrich at uwa.edu.au>

Graduate School of Education
The University of Western Australia
M428, 35 Stirling Highway,
Western Australia , 6009

Telephone: +61 8 6488 1085
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Pearson Psychometric Laboratory<blocked::http://www.education.uwa.edu.au/ppl>
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From: rasch-bounces at acer.edu.au [mailto:rasch-bounces at acer.edu.au] On Behalf Of Anthony James
Sent: Tuesday, 12 June 2012 10:56 PM
To: Rasch at acer.edu.au
Subject: [Rasch] Rsch and CFA

Dear colleagues,
I have some questions on Rasch and other latent trait models.
Please help clarify things for me.

1.      In latent trait models based on CTT there is always an error term in the equations. But in formulations of Rasch and IRT models there is no room for error.  Why? Why don't we assume that in the responses to items error also plays a role?
2.      Is there any proof in the Rasch and IRT models to show that observed item responses are CAUSED by the latent variable. I mean is there a proof to establish a causal relationship between observed and latent variables?
3.      Why aren't confirmatory  factor analysis and structural equation modeling used as measurement models in the way IRT models are used. I mean why don't CFA people base person scores on factor scores from CFA?

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