Contents
What is differential item functioning analysis?
Differential item functioning (DIF) methods are a range of techniques that are increasingly being used to evaluate whether different subgroups respond differently to particular items within a scale, after controlling for group differences in the overall HRQoL domain being assessed.
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When does DIF occur in differential item functioning?
In Differential Item Functioning (eds. Holland & Wainer, 1993), Angoff explains that DIF is occurring when an item displays different statistical properties between groups after those groups have been matched on a measure of proficiency.
How is DIF used in item retention decisions?
Another area of item performance that is often used for item retention decisions is item bias, commonly referred to as differential item functioning (DIF). DIF studies are generally implemented to see how the performances of two groups compare on a single item in an assessment (though studies can be done with more than two groups).
What does uniform DIF mean in item analysis?
Uniform DIF indicates that one group is (on average) always at a disadvantage when responding to the item. If we were to create item characteristic curves for the two groups, they would not intersect. Non-uniform DIF means that one group has an advantage for some proficiency levels, but is at a disadvantage at other proficiency levels.
Which is the best method for item analysis?
One simple method that some practitioners use is based on the four-fifths rule, which is detailed in the Uniform Guidelines for Employee Selection Procedures. This method involves comparing the correct response rates ( p values) for the two groups.