The Effect Size for Simultaneous Item Bias Test

• Activity Number: 345
• Type: Contributed
• Date/Time: Tuesday, August 5, 2014 : 10:30 AM to 12:20 PM
• Sponsor: Social Statistics Section
• Author(s): Zhushan Li*+
• Companies: Boston College
• Keywords: DIF ; item response theory ; measurement bias ; effect size

Abstract

Differential item functioning (DIF) occurs when people from different groups with the same level of latent trait (ability/skills) have a different probability of responding to an item or a bundle of items in a questionnaire or test. DIF detection is an important step in the evaluation of the measurement bias in an instrument. Simultaneous Item Bias Test (SIBTEST, Shealy & Stout 1993) is a popular DIF detection method which can handle both dichotomous and polytomous items, and DIF in a single item and in a bundle of items. In this paper, we focus on the effect size measure as defined SIBTEST, and derive the formulas for the effect size under the IRT models. The relationship between the SIBTEST effect size and other popular DIF effect size measures are discussed. The correctness of the formula is confirmed by simulation studies.