[Rasch] Rsch and CFA

Anthony James luckyantonio2003 at yahoo.com
Wed Jun 13 00:55:47 EST 2012

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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