The IRT Procedure

MODEL Statement

MODEL model-specification <, model-specification …>;

where model-specification is defined as variable-list < / model-option > The MODEL statement specifies the items and their response functions or models. You can specify different response models for different items. In the variable-list, you specify the set of variables that use the same model.

You can specify the following model-option:

RESFUNC < = [ response-model-types ] >: specifies the response function or model. For available keywords, see the RESFUNC= option in the PROC IRT statement. For technical details about these response models, see "Response Models" in the section Details: IRT Procedure.

You can specify mixed response models for different items as follows:

proc irt;
   model x1-x10/resfunc=twop, x11-x20/resfunc=graded, x21-x30/resfunc=threep;
run;

For variables that are also listed in the VAR statement, the model that is specified here overwrites the default model or the model that is specified by using the RESFUNC= option in the PROC IRT statement.

You can use the EQUALITY statement to set equality constraints on these parameters.