This is the webpage for the handbook on differential item functioning.

Zumbo, B. D. (1999). A Handbook on the Theory and Methods of Differential Item Functioning (DIF): Logistic Regression Modeling as a Unitary Framework for Binary and Likert-type (Ordinal) Item Scores. Ottawa ON: Directorate of Human Resources Research and Evaluation, Department of National Defense.

Because I wrote the Handbook under a research contract from the Department of National Defense (DND) of Canada, the DND is distributing it free of charge for purposes of research and teaching.

The Handbook is available below in PDF format and can be accessed with Acrobat Reader. The example data files and SPSS syntax command files are also available below.

If you prefer a bound hard copy of the handbook please contact Professor Zumbo via e-mail. The e-mail address is listed below.

If you have problems retrieving any of the files below or you want to contact Professor Zumbo at the Edgeworth Laboratory for Quantitative Educational & Behavioral Science, you can do so by the post or via Internet e-mail:

1. To access (for printing or reading on screen) a copy of the Handbook with Adobe Acrobat Reader please click here.

2. A copy of the SPSS syntax files and the example data sets are available in a compressed (zipped file) can be found here.

3. You can also download a more recent description by Slocum, Gelin, and Zumbo of how to do DIF analyses in SPSS here.

If you have difficulty downloading files, please contact Professor Zumbo at e-mail:

Updated: September 1, 2017