New Features
Exporting IRTPRO spreadsheet files (*.ssig) to SPSS, SAS, STATA, etc. formats

This feature is now available in IRTPRO 4 and is accomplished as follows:

  • Use the File, Open option to open an .ssig file
  • Use the File, Export option to export this file to a different format

Example

Assume we want to export Anxiety14.ssig to the SPSS .sav format. Use the File, Open option to locate and select this file.

Click the Open button to display the following spreadsheet:

Select the File, Export option:

From the drop-down list, select SPSS Data File(*.sav).

 The Save As dialog enables one to save the file in any folder. The default folder is the one where the .ssig file is located and the default name is that of the .ssig file.  

 

Fixed Theta Estimation

The purpose of fixed theta estimation is to specify the computation of the item parameters with respect to an external variable, the values of which are supplied in the data records, rather than to a latent variable inferred from the item responses. When item parameters are estimated in this way and used to score test data of any other groups of examinees, the resulting scores are the best predictors of the ability measured by the external variable.

In each record of the calibration data, each test in the analysis must be represented by a value of the external variable. In the multidimensional case, the number of external variables must be equal to the number of dimensions. 

Note that the estimation of fixed effects is only available when MH-RM is selected as the method of estimation. In this case, the Fixed Theta tab on the advanced options dialog is activated and the variable(s) can be selected from the IRTPRO spreadsheet (*.ssig) file that contains the item responses and external variable values.

As an example, suppose a group of students took an end-of-term reading test and math test routinely administered to all students in a metropolitan school district. Suppose these students were also part of the sample for a state assessment of reading and math achievement. If scores and standard errors on the assessment tests for these students were available to the district, the district test could be calibrated to best predict the state reading and math scores of students of all students in the district. For this purpose, the state test results would serve as the external variables for calibrating items of the local tests to predict the state assessment’s scores.

Chapter 10 of the IRTPRO 4 guide contains a multidimensional, multiple groups example and additional examples are provided in the IRTPRO 4 Examples\Fixed Theta folder.

Graphical display of continuous variables

The Graphics, Continuous… option allows us to graphically display the distribution of one or more continuous variables. In the case of more than one group, the distributions across groups are overlaid on the same axis system.

 

 Selection of this option results in the display of a Continuous Graph dialog, allowing the user to select a Group-variable and one or more Continuous-variables to obtain set of distributions:

See Section 13.4 of the IRTPRO 4 guide for a more detailed description.

Simulation when only a parameter file is available

In practice, many datasets are regarded as confidential and can not be made available to researchers not affiliated with the organization that owes the data. However, estimation results are often available in the form of a publication or these results can be shared in the form of an IRTPRO parameter file.

 To simulate data using this parameter file, we start by generating a “fake” dataset that will contain the parameter names, category values and allow us to specify the sample size for each group. This is accomplished by selecting the File, Create SSIG for Simulation option as shown below. 

 

 By selecting this option, a Create SSIG for Simulation dialog is activated. Browse for the parameter file. The .ssig file will have the same name, but with extension –gen.ssig.

This procedure is discussed and illustrated in Section 9.3 of the IRTPRO 4 guide.

Appearance of syntax file and addition of the Find function on the Edit Menu

When a syntax file is based on a large number of items and groups, locating specific paragraphs can be tedious and could be missed when scrolling fast through the .irtpro file.

To make it easier to locate specific sections in the syntax file, an Edit, Find option has been added and the name of each section is shown in blue as shown next.