Useful Reporting of DIF

Major problems with the investigation of differential item functioning (DIF, item bias) are inexplicability and unreproducibility. Merely relying on statistical indicators to identify DIF leaves the analyst at the mercy of idiosyncratic samples of sub-groups. Experts, on the other hand, can discover something biased in every test item. Different experts can even assert that items are biased in different directions!

A combination of statistical, substantive and graphical techniques solves this problem. The Figure illustrates DIF in an "activities of daily living" (ADL) instrument. Looking at an single item, such as "Small-scale Shopping", we could come up with reasons why it is biased against both men and women! But plot all the item difficulties for men against those for women, and the general pattern is clear. Men find it harder to do chores around the house, "Washing", "Cleaning", "Cooking". Women find gross motor activities harder, "Locomotion Outdoors", "Small-scale shopping", "Large-scale shopping". Neutral items are "Simple meal" and "Public transport". Since the bias pattern indicated statistically has a clear substantive meaning that surmounts individual items, we can report the DIF as explicable and likely to be reproduced in continuing use of the instrument.

Gunnar Grimby

Grimby G., Andrén E., Daving Y., Wright B.D. (1998) Dependence and perceived difficulty in daily activities in stroke survivors. Stroke 29, 1843-1849.

Useful reporting of DIF.Grimby G. … Rasch Measurement Transactions, 1998, 12:3 p. 651.

Rasch Publications
Rasch Measurement Transactions (free, online) Rasch Measurement research papers (free, online) Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch Applying the Rasch Model 3rd. Ed., Bond & Fox Best Test Design, Wright & Stone
Rating Scale Analysis, Wright & Masters Introduction to Rasch Measurement, E. Smith & R. Smith Introduction to Many-Facet Rasch Measurement, Thomas Eckes Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr. Statistical Analyses for Language Testers, Rita Green
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Journal of Applied Measurement Rasch models for measurement, David Andrich Constructing Measures, Mark Wilson Rasch Analysis in the Human Sciences, Boone, Stave, Yale
in Spanish: Análisis de Rasch para todos, Agustín Tristán Mediciones, Posicionamientos y Diagnósticos Competitivos, Juan Ramón Oreja Rodríguez

To be emailed about new material on
please enter your email address here:

I want to Subscribe: & click below
I want to Unsubscribe: & click below

Please set your SPAM filter to accept emails from welcomes your comments:

Your email address (if you want us to reply):


ForumRasch Measurement Forum to discuss any Rasch-related topic

Go to Top of Page
Go to index of all Rasch Measurement Transactions
AERA members: Join the Rasch Measurement SIG and receive the printed version of RMT
Some back issues of RMT are available as bound volumes
Subscribe to Journal of Applied Measurement

Go to Institute for Objective Measurement Home Page. The Rasch Measurement SIG (AERA) thanks the Institute for Objective Measurement for inviting the publication of Rasch Measurement Transactions on the Institute's website,

Coming Rasch-related Events
June 23 - July 21, 2023, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps),
Aug. 11 - Sept. 8, 2023, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets),


The URL of this page is