The IRT Procedure

Output Data Sets

Subsections:

OUTMODEL= Data Set

The OUTMODEL= data set contains the model specification, the computed parameter estimates, and the standard error estimates. This data set is intended to be reused as an INMODEL= data set in a subsequent analysis by PROC IRT.

The OUTMODEL= data set contains the following variables:

  • BY variables, if any

  • _GPNUM_ variable for group numbers, if used

  • _TYPE_, a character variable that takes various values that indicate the type of model specification

  • _SUBTYP_, a character variable that takes various values that indicate the type of model parameters

  • _NAME_, a character variable that indicates the model type, parameter name, or variable name

  • _NUM_, a numeric variable that takes various values that indicate model specifications such as the number of items, number of factors, number of groups, and number of levels for each item

  • _VAR1_, a character variable that is the name or number of the first variable in the specification

  • _VAR2_, a character variable that is the name or number of the second variable in the specification

  • _ESTIM_, a numeric variable that is the final estimate of the parameter

  • _STDERR_, a numeric variable that is the standard error estimate of the parameter

Each observation (record) of the OUTMODEL= data set contains a piece of information about the model specification. Depending on the type of specification that the value of the _TYPE_ variable indicates, the meanings of the _SUBTYP_, _NAME_, _NUM_ _VAR1_, and _VAR2_ variables differ. Table 65.3 summarizes the meanings of these variables for each value of the _TYPE_ variable.

Table 65.3: Meaning of Variables in the OUTMODEL=Data Set

_TYPE_

Description

_SUBTYP_

_NAME_

_NUM_

_VAR1_

_VAR2_

MODEL

Model Info

 

NGROUP

Number of groups

    

MODEL

Model Info

 

NITEM

Number of items

    

MODEL

Model Info

 

NFACTOR

Number of factors

    

MODEL

Model Info

 

LINK

 

Link function

 

MODEL

Model Info

 

RORDER

 

RORDER option

 

MODEL

Model Info

 

DESC

 

DESC option

 

VAR

Variable

 

Name

Number of levels

Response function

 

FACTOR

Factor

 

Name

     

GPVAR

Group

 

Group var name

     

PARM

Parameter

CEILING

Name

Number

Variable

 

PARM

Parameter

GUESSING

Name

Number

Variable

 

PARM

Parameter

INTERCEPT

Name

Number

Variable

Category

PARM

Parameter

SLOPE

Name

Number

Variable

Factor

PARM

Parameter

COV

Name

Number

1st variable

2nd variable

PARM

Parameter

MEAN

Name

Number

Variable

 


For computational convenience, the intercept parameters rather than the threshold (or difficulty) parameters are saved in the OUTMODEL= data set. For multidimensional exploratory analysis, the OUTMODEL= data set includes the unrotated factor loading matrix. In the OUTMODEL= data set, fixed parameters do not have names but only parameter numbers. For free parameters, the OUTMODEL= data set includes the parameter name and the parameter number. When this data set is used for the INMODEL= option, PROC IRT sets an equality constraint for parameters that have the same name.