[Rasch] Modeling response time

Stuart Luppescu lupp at uchicago.edu
Fri Feb 3 06:55:29 AEDT 2017


On Tue, 2017-01-31 at 19:00 -0200, Ricardo Primi wrote:
> Hi Stuart
> I guess that you don’t want to model interaction . You want to model
> main effects of item and person to and then inspect the residuals
> trying to see who is far off the predicted RT from 
> this model considering additive main effects  right? Besides
> including interaction make this model  non-identified because you
> have an interaction parameter for each combination of personX item
> (minos 1)
> 
> Usually IRT models are just main effects models (person as a random
> variable and item as fixed or sometimes random variables).
> Interactions are used to assess DIF. In this case you have several
> items from the same group and this makes the identification of
> interaction possible (you have the same interaction parameter for th
> items of the same group)
> 
> So i think the model would be :
> 
> lmer(log(answer_time) ~ qid + (1|examinee), data=test.DF, REML=FALSE)
> 
> And then examine the residuals after fitting this model

This worked great! Thanks very much, Ricardo.
-- 
Stuart Luppescu
Chief Psychometrician (ret.)
UChicago Consortium on School Research
http://consortium.uchicago.edu

lupp at uchicago.edu


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