[Rasch] computing outfit mean-squares for each rating category in eRm (PCM)
trevor.bond at jcu.edu.au
Tue Aug 9 18:28:27 AEST 2016
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?
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