Non-uniform DIF ICCs

Non-uniform DIF ICCs (non-uniform Differential Item Functioning Item Characteristics Curves) are also called Group Empirical IRFs (Item Response Functions) and Group Trace Lines. These are displayed for items. To see non-uniform DPF (person) ICCs, first transpose the data, then display these with the persons as items. Non-uniform DIF can also be investigated numerically using Winsteps Table 30..

 

 

Click on "Display by item" and "Display enhanced graph".. Select the Non-Uniform DIF ICCs option on the Graphs menu.

 

 

Confirm the columns in the person label of the DIF= group classification.

 

 

Your screen reports that the DIF information is being collected from the data file.

 

In the Graph window, click on "Non-Uniform ICCs"

 

 

The DIF selection dialog box displays:

 

 

Choose which curves you want to see by clicking in a box. The box turns green with the letter "x".

 

 

 

Here, the model ICC (red) for the item and the uniform (smooth) and non-uniform (jagged) DIF curves (blue) for the "M" person group  are shown.

 

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For Standard graphing:

 

Double-click on unwanted lines to remove them. Here only the non-uniform DIF line for the F group is shown.