R help - Jul 2010 - DIF Analysis starting from a gpcm class object

Dear useRs,

does any of you have suggestions on how to conduct a proper DIF analysis
starting from a model of
class gpcm (from the wonderful package ltm by prof. Rizopoulos)? 

difR will handle only dichotomous items, and I have a mix of dicho- and
polytomous ones (that's why I chose the partial credit model). 

I also found the package lordif, but I'm not really sure if that's what
I
need.

I basically want to regress item difficulties on some other covariates (sex,
age class,...)..

Is there a package you know of that handle such models for a DIF analysis or
should I code such a thing by myself? and if so, how can I extract what I
need from the model object?

thanks to everybody

/federico

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Dr. Federico Andreis
Universit? degli Studi di Milano-Bicocca, PhD Student
MEB Department, Karolinska Institutet, Stockholm, Visiting PhD Student
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Problem: To Catch a Lion in the Sahara Desert - The Dirac Method 

We observe that wild lions are, ipso facto, not observable in the Sahara
Desert. Consequently, if there are any lions in the Sahara, they are tame.
The capture of a tame lion may be left as an exercise for the reader.
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