Differential Item Functioning

[Page 440]Differential item functioning (DIF) is a phenomenon in which a test or survey item performs differently based on the respondent who is using it, and this difference in performance is unrelated to the latent concept the item is intended to measure. For example, a test item might be more difficult for a male student than a female student even if both students have the same ability (and have gotten the same total score on the test). An example of DIF in a survey context would be, when using a 5-point Likert-type scale, one respondent’s “4” might be another respondent’s “5,” because of question or scale wording, though both respondents perceive the same latent value of the concept the scale is measuring.

The implications of DIF ...