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

Bond, Trevor trevor.bond at jcu.edu.au
Tue Aug 9 18:28:27 AEST 2016

Dear Alex
In what sense do you judge the PCM to have better fit? The RSM is much more parsimonious. Remember Occam's Razor.

Sent from 007's new iPhone 6s ?

On 8 Aug 2016, at 5:16 PM, Alexandra Dima <alexadima at gmail.com<mailto:alexadima at gmail.com>> wrote:

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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