mixing items with different format

[Asghar Minaei]

Hello Dear Philip

I'm using mirt to analysis  a test which contains 10 dichotomous(0,1) and 5 polytomous items which scored as 0,1, and 2. I'm attempting to use a combination of  simple Rasch  and Rating Scale Models.

 I run the following codes:

items<-rep("Rasch", 15)
items[11:15]<-"rsm"
rasch.model<-"F= 1-15"
rasch.fit<-mirt(A_data[,3:17], model= rasch.model, itemtype = items, SE=TRUE)
rasch.para<-coef(rasch.fit, IRTpars=TRUE, simplify=TRUE, printSE=TRUE

and I get this error:

Error: Rating scale models require that items to have the
                                        same number of categories

 Any help from you would be appreciated! Thanks in advance

regards

Asghar

[Phil Chalmers]

Hi Asghar,

This error seems a little aggressive from mirt() and should probably be patched. For now you can use the rsm.block vector input to specify which items should belong to which block. For now, just treat the real rating scale items as a unique block, and the other items as a separate block. I'll try to make a patch for this though in the next version since this does seem like a false cause for concern. Thanks.

Phil

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[Phil Chalmers]

Patch is now available on the Github dev version. If you install that first your current code should work fine. HTH.

Phil