Differential Item Functioning (DIF)
A psychometric phenomenon where a test item behaves differently across demographic groups (gender, culture, language) holding the underlying trait constant. A key fairness check.
DIF analysis asks: do test takers with the same true level of the trait — but from different demographic groups — answer this specific item differently? If yes, the item is biased and undermines test fairness.
Example: a Big Five item about "enjoying parties" may show DIF between cultures with different default social structures, even when underlying Extraversion is held constant. Such items are flagged and either revised or removed from cross-cultural use.
Modern test development (IRT-based, large samples) routinely screens for DIF before release. JobCannon's test development pipeline checks DIF for English-language items across major subgroups; items showing significant DIF are revised or replaced.
Source: Holland & Wainer (1993). Differential Item Functioning. Hillsdale, NJ: Erlbaum.