Differential item functioning

Differential item functioning or group- dependent indicator is a term used in psychological assessment that has arisen from the application of psychological instruments in different cultures or subcultures, and is intended to describe different response in groups on the same questions. Group dependency is created when people from different groups (mostly gender or ethnicity) with the same personality characteristics or with the same ability have a different probability of giving a certain response to a questionnaire or a test.

The analysis of group dependence allows an indication of unexpected behavior in terms of an indicator (item). An indicator has no zoning when people from different groups have different response probabilities, however, it has then group depending on when people from different groups with the same underlying characteristics of the property have a different probability of giving a certain answer.

The analysis and correction of the group depending particularly plays a role in so-called high stakes testing, where not only out of interest one property is measured, but a selection decision on various language areas is carried away, such as at study space management in multilingual countries, such as as Switzerland, Canada, Italy, etc.

Example

In Germany far carried out a knowledge test among students the following question is used to query the geographic knowledge, "What is the capital of Hessen" Hessian students have an advantage, as they are much more likely to know the capital of their own state. The indicator is thus dependent group and the test result would falsely give the impression that Hessian students have better geographical knowledge than students from other states.