[Rasch] computing outfit mean-squares for each rating category in eRm (PCM)

Alexandra Dima alexadima at gmail.com
Tue Aug 9 01:16:25 AEST 2016

Dear Rasch colleagues, 


I am trying to replicate a Rasch analysis performed with WINSTEPS. 

They examine the item rating structure of an 8-item questionnaire (5-point Likert response format). 

One criterion they consider is that the outfit mean-squares are <2.0 for each rating category. 


I am using the eRm package in R – the RSM and PCM functions. 

PCM fits better, so I use it for examining item properties etc.

I can find item outfit and infit, but not outfit mean-squares for each rating category.

There must be a way to get it (I see the infit t statistic for each category in the Item Map via the plotPWmap function).


Any suggestions on how I can compute these?


Many thanks, 


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