Rating Scale Examples

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Rasch Property of Invariance Item difficulty measure should remain constant no matter the population taking the assessment. If an item difficulty measure is different for two groups of students, that item is said to exhibit Differential Item Functioning (DIF). As defined by Clauser and Mazor (1998), “Differential item functioning is present when examinees from different groups have differing probabilities of or likelihoods of success on an item” (p. 31). With the Rasch model, each examinee has ability, and each item has difficulty. If DIF exists, item difficulty for the reference and focus groups will be different. “The comparison of difficulty for the focus and reference groups can be calculated from all, or any convenient subset, of the reference and focus groups (Linacre & Wright, 1987, p. 11).

Bias measuring persons unfairly based on race, sex, or cultural background Is an item that exhibits DIF biased? For a couple of examples:

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