[Rasch] Rsch and CFA

Rense Lange rense.lange at gmail.com
Wed Jun 13 04:53:02 EST 2012

Regarding 1: Sure there is an error term, it follows directly from Rasch models' probabilistic nature. The model gives the probabilities of getting one item correct and from there one can compute the probabilities of getting any number items correct in a set, and from there one can obtain (e.g, via bootstrapping) the likely error in the Rasch measure. Of course Winsteps already told you the answer you will get ...

On Jun 12, 2012, at 9:55 AM, Anthony James wrote:

> 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?
> Cheers
> Anthony
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