Seminar in Psychometrics

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Equating and DIF detection in the IRT framework

Date and time: March 31, 2022 (2:30 PM CET)
Place Remotely on Zoom.

Abstract. Differential Item Functioning (DIF) occurs when the probability of a positive response for people at the same ability level varies in different groups of individuals. The detection of DIF is very important since it constitutes a violation of the invariance assumption of Item Response Theory (IRT) models. One approach for the detection of DIF is based on the comparison of the item parameter estimates obtained in different groups of the population. However, when the item parameters are estimated separately, they are expressed on different measurement scales, due to identifiability issues. So, it is first necessary to convert the item parameter estimates to a common scale. This transformation involves two unknown constants, called equating coefficients, which are estimated from the data. The item parameter estimates converted to a common metric are then compared through a statistical test. The test implemented in the R package equateIRT takes into account the variability introduced by the estimation of the equating coefficients, thus improving the properties of the test. In this talk, the methods for the estimation of the equating coefficients will be reviewed and a test for the detection of DIF will be presented. The methods will be illustrated using the equateIRT package.

Michaela Battauz
University of Udine