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The Generalized Partial Credit Model in PROC IRT

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New Contributor
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The Generalized Partial Credit Model in PROC IRT

Is the Generalized Partial Credit really available in PROC IRT?  

 

What’s New in SAS/STAT 14.1 states that 

The generalized partial credit (GPC) model is available for ordinal items

 

The Response Models part of the Details section states that

PROC IRT supports several response models for binary and ordinal responses, and it allows different items to have different response models. Details about these response models and their relationships follow:

...

•Generalized partial credit model: This model assumes that items are ordinal-categorical with at most 19 levels. The slopes (or discrimination) and the step parameters of the items are free parameters in the model.

 

In addition, the EQUALITY subcommand includes the following possible specifications:

...

_ALLGPC_
_ALLGPCITEM_
specifies all variables that are fitted by the generalized partial credit model in the analysis. 

...

_ALLGPC_BUT_ [ excluded-variables ]
_ALLGPCITEM_BUT_ [ excluded-variables ]
specifies all variables except the excluded-variables that are fitted by the generalized partial credit model in the analysis.

 

However, a corresponding RESFUNC= option fof the model is not included in the syntax documentation for the MODEL subcommand. Are these all documenatation errors?

 

 

 

 

 

 

 

Grand Advisor
Posts: 16,933

Re: The Generalized Partial Credit Model in PROC IRT


joseph0 wrote:

Is the Generalized Partial Credit really available in PROC IRT?  

 

 ...

However, a corresponding RESFUNC= option fof the model is not included in the syntax documentation for the MODEL subcommand. Are these all documenatation errors?

 

 


Are you referring to the prompts/autocomplete when you're typing in EG or SAS Studio?

If so, it's not always up correct. 

 

The online documentation does list RESFUNC= as an option.

http://support.sas.com/documentation/cdl/en/statug/68162/HTML/default/viewer.htm#statug_irt_syntax16...

 

New Contributor
Posts: 4

Re: The Generalized Partial Credit Model in PROC IRT

The only RESFUNC option for ordinal items is GRADED for the Graded Response Model.  There is nothing for the Generalized Partial Credit Model. 

SAS Super FREQ
Posts: 3,319

Re: The Generalized Partial Credit Model in PROC IRT

[ Edited ]

Thank you for reporting this documentation omission. It has already been fixed. The updated documentation will be available in the next release.

 

The answer to your question is that you need to use the RESFUNC=GPC option.

 

You can actually use SAS's error processing to tell you the valid values of any SAS option. Just specify an invalid option and then look in the SAS log to discover the valid options.  For example, if you submit this SAS code:

proc irt data=mydata;
   var item1-item10;
   model item1-item4/resfunc=JUNK;
run;

 

then the SAS log reports the following error:

1833 model item1-item4/resfunc=JUNK;
                               ----

                               22
ERROR 22-322: Syntax error, expecting one of the following:
FOURP, GPC, GRADED, NOMINAL, ONEP, RASCH, THREEP, TWOP.

You can see that the option that you need in specified in the list of possible values, and from the name you can guess that this is the option for Generalized Partial Credit.

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