Sample interview questions: Can you explain the concept of differential item functioning (DIF) and how it is assessed in the assessment of cognitive impairments?
Sample answer:
Differential item functioning (DIF) refers to the phenomenon in which items on a cognitive assessment instrument perform differently for different groups of individuals despite having the same underlying ability level. This can lead to biased measurement and inaccurate conclusions about individuals’ cognitive abilities.
DIF is assessed using statistical methods that compare the performance of different groups on individual items, while controlling for overall ability level. Common methods include:
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Mantel-Haenszel Method: This method compares the performance of two groups on an item, taking into account the overall ability distribution of the groups. If the performance of one group is significantly different from the other group, DIF is indicated.
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Item Response Theory (IRT) Methods: IRT models can be used to estimate individual item parameters, including the difficulty and discrimination parameters. DIF can be detected by comparing the item parameters for different groups.
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Logistic Regression: Logistic regression can be used to model the probability of answering an item correctly as a function of group membership and other relevant variables. DIF is indicated if group membership is a significant predictor of item performance, even after controlling for ability level.
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