[Rasch] Rsch and CFA

Swank, Paul R Paul.R.Swank at uth.tmc.edu
Wed Jun 13 02:02:53 EST 2012

I would say that, 1 there is error in the Rasch model in terms of the discrepancy between what the model predicts and the actual response; 2) no model can prove that the response is caused by the latent variable. All latent variables are inferred; and 3), there is a factor analytic measurement model. See Raykov & Marcoulides, Introduction to psychometric Theory. Mplus does a one or two parameter model (depending on how you specify it) in CFA when you specify the items as discretely but ordered.

Paul R. Swank, Ph.D.
Professor, Department of Pediatrics
Medical School
Adjunct Professor, Health Promotions and Behavioral Sciences
School of Public Health
University of Texas Health Science Center at Houston

From: rasch-bounces at acer.edu.au [mailto:rasch-bounces at acer.edu.au] On Behalf Of Anthony James
Sent: Tuesday, June 12, 2012 9:56 AM
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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