Differential item functioning

Differential item functioning (DIF) is when a test question or item works differently for different groups of people because of factors like gender, ethnicity, or language. Imagine you and your friend are taking a test, and there is a question that asks what your favorite animal is. You answer "dog" and your friend answers "cat," but the test thinks your answer is better than your friend's answer just because you are a boy and your friend is a girl.

To make sure that the items in a test are fair for everyone, researchers use statistical methods to detect DIF. These methods compare the test scores of different groups of people who have taken the same test and see if certain items work differently for those groups. If they find DIF, they may change or remove the items to make the test fairer.

DIF is important because it affects the validity and reliability of the test. A test that has DIF can unfairly advantage or disadvantage certain groups of people, leading to biased results. By detecting and correcting DIF, we can create tests that accurately measure what they are supposed to measure, and help people succeed based on merit rather than their background.